draft-ietf-httpbis-bcp56bis-02.txt   draft-ietf-httpbis-bcp56bis-03.txt 
HTTP M. Nottingham HTTP M. Nottingham
Internet-Draft February 28, 2018 Internet-Draft April 2, 2018
Obsoletes: 3205 (if approved) Obsoletes: 3205 (if approved)
Intended status: Best Current Practice Intended status: Best Current Practice
Expires: September 1, 2018 Expires: October 4, 2018
On the use of HTTP as a Substrate On the use of HTTP as a Substrate
draft-ietf-httpbis-bcp56bis-02 draft-ietf-httpbis-bcp56bis-03
Abstract Abstract
HTTP is often used as a substrate for other application protocols. HTTP is often used as a substrate for other application protocols.
This document specifies best practices for these protocols' use of This document specifies best practices for these protocols' use of
HTTP. HTTP.
This document obsoletes RFC 3205.
Note to Readers Note to Readers
Discussion of this draft takes place on the HTTP working group Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/ [1]. https://lists.w3.org/Archives/Public/ietf-http-wg/ [1].
Working Group information can be found at http://httpwg.github.io/ Working Group information can be found at http://httpwg.github.io/
[2]; source code and issues list for this draft can be found at [2]; source code and issues list for this draft can be found at
https://github.com/httpwg/http-extensions/labels/bcp56bis [3]. https://github.com/httpwg/http-extensions/labels/bcp56bis [3].
skipping to change at page 1, line 43 skipping to change at page 1, line 45
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 1, 2018. This Internet-Draft will expire on October 4, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 4 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 4
2. Is HTTP Being Used? . . . . . . . . . . . . . . . . . . . . . 4 2. Is HTTP Being Used? . . . . . . . . . . . . . . . . . . . . . 4
3. What's Important About HTTP . . . . . . . . . . . . . . . . . 5 3. What's Important About HTTP . . . . . . . . . . . . . . . . . 5
3.1. Generic Semantics . . . . . . . . . . . . . . . . . . . . 5 3.1. Generic Semantics . . . . . . . . . . . . . . . . . . . . 5
3.2. Links . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2. Links . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Getting Value from HTTP . . . . . . . . . . . . . . . . . 6 3.3. Rich Functionality . . . . . . . . . . . . . . . . . . . 7
4. Best Practices for Using HTTP . . . . . . . . . . . . . . . . 7 4. Best Practices for Using HTTP . . . . . . . . . . . . . . . . 7
4.1. Specifying the Use of HTTP . . . . . . . . . . . . . . . 7 4.1. Specifying the Use of HTTP . . . . . . . . . . . . . . . 8
4.2. Defining HTTP Resources . . . . . . . . . . . . . . . . . 8 4.2. Defining HTTP Resources . . . . . . . . . . . . . . . . . 8
4.3. Specifying Client Behaviours . . . . . . . . . . . . . . 9 4.3. Specifying Client Behaviours . . . . . . . . . . . . . . 9
4.4. HTTP URLs . . . . . . . . . . . . . . . . . . . . . . . . 10 4.4. HTTP URLs . . . . . . . . . . . . . . . . . . . . . . . . 10
4.4.1. Initial URL Discovery . . . . . . . . . . . . . . . . 10 4.4.1. Initial URL Discovery . . . . . . . . . . . . . . . . 11
4.4.2. URL Schemes . . . . . . . . . . . . . . . . . . . . . 10 4.4.2. URL Schemes . . . . . . . . . . . . . . . . . . . . . 11
4.4.3. Transport Ports . . . . . . . . . . . . . . . . . . . 12 4.4.3. Transport Ports . . . . . . . . . . . . . . . . . . . 12
4.5. HTTP Methods . . . . . . . . . . . . . . . . . . . . . . 12 4.5. HTTP Methods . . . . . . . . . . . . . . . . . . . . . . 12
4.6. HTTP Status Codes . . . . . . . . . . . . . . . . . . . . 12 4.5.1. GET . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.7. HTTP Header Fields . . . . . . . . . . . . . . . . . . . 13 4.6. HTTP Status Codes . . . . . . . . . . . . . . . . . . . . 14
4.8. Defining Message Payloads . . . . . . . . . . . . . . . . 15 4.7. HTTP Header Fields . . . . . . . . . . . . . . . . . . . 15
4.9. Authentication and Application State . . . . . . . . . . 15 4.8. Defining Message Payloads . . . . . . . . . . . . . . . . 16
4.10. Co-Existing with Web Browsing . . . . . . . . . . . . . . 15 4.9. HTTP Caching . . . . . . . . . . . . . . . . . . . . . . 16
4.11. Co-Existing with Other Applications . . . . . . . . . . . 16 4.10. Application State . . . . . . . . . . . . . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 4.11. Client Authentication . . . . . . . . . . . . . . . . . . 17
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16 4.12. Co-Existing with Web Browsing . . . . . . . . . . . . . . 18
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 4.13. Application Boundaries . . . . . . . . . . . . . . . . . 19
7.1. Normative References . . . . . . . . . . . . . . . . . . 17 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
7.2. Informative References . . . . . . . . . . . . . . . . . 19 6. Security Considerations . . . . . . . . . . . . . . . . . . . 20
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 21 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
Appendix A. Changes from RFC3205 . . . . . . . . . . . . . . . . 21 7.1. Normative References . . . . . . . . . . . . . . . . . . 20
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21 7.2. Informative References . . . . . . . . . . . . . . . . . 22
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Appendix A. Changes from RFC 3205 . . . . . . . . . . . . . . . 25
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
HTTP [RFC7230] is often used as a substrate for other application HTTP [RFC7230] is often used as a substrate for other application
protocols. This is done for a variety of reasons, including: protocols. This is done for a variety of reasons, including:
o familiarity by implementers, specifiers, administrators, o familiarity by implementers, specifiers, administrators,
developers and users, developers and users,
o availability of a variety of client, server and proxy o availability of a variety of client, server and proxy
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o ease of use, o ease of use,
o ubiquity of Web browsers, o ubiquity of Web browsers,
o reuse of existing mechanisms like authentication and encryption, o reuse of existing mechanisms like authentication and encryption,
o presence of HTTP servers and clients in target deployments, and o presence of HTTP servers and clients in target deployments, and
o its ability to traverse firewalls. o its ability to traverse firewalls.
The Internet community has a long tradition of protocol reuse, dating In many cases, these protocols are ad hoc; they are intended for only
back to the use of Telnet [RFC0854] as a substrate for FTP [RFC0959] deployment on the server side, and consumption by a limited set of
and SMTP [RFC2821]. However, layering new protocols over HTTP brings clients. A body of practices and tools has arisen around defining
its own set of issues: such "HTTP APIs" that favours these conditions.
However, when such a protocol is standarised, it is typically
deployed on multiple servers, implemented a number of times, and
might be consumed by a broader variety of clients. Such diversity
brings a different set of concerns, and tools and practices intended
for a single-server deployment might not be suitable.
In particular, standards-defined HTTP APIs need to more carefully
consider how extensibility and evolution will be handled, how
different deployment requirements will be accommodated, and how
clients will evolve with the API.
At the same time, the Internet community has a tradition of protocol
reuse (e.g., Telnet [RFC0854] as a substrate for FTP [RFC0959] and
SMTP [RFC2821]), but less experience using HTTP as a substrate.
Because HTTP is extensible in many ways, a number of questions arise,
such as:
o Should an application using HTTP define a new URL scheme? Use new o Should an application using HTTP define a new URL scheme? Use new
ports? ports?
o Should it use standard HTTP methods and status codes, or define o Should it use standard HTTP methods and status codes, or define
new ones? new ones?
o How can the maximum value be extracted from the use of HTTP? o How can the maximum value be extracted from the use of HTTP?
o How does it coexist with other uses of HTTP - especially Web o How does it coexist with other uses of HTTP - especially Web
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3.1. Generic Semantics 3.1. Generic Semantics
When writing an application's specification, it's often tempting to When writing an application's specification, it's often tempting to
specify exactly how HTTP is to be implemented, supported and used. specify exactly how HTTP is to be implemented, supported and used.
However, this can easily lead to an unintended profile of HTTP's However, this can easily lead to an unintended profile of HTTP's
behaviour. For example, it's common to see specifications with behaviour. For example, it's common to see specifications with
language like this: language like this:
A `200 OK` response means that the widget has successfully been updated. A `200 OK` response means that the widget has successfully been
updated.
This sort of specification is bad practice, because it is adding new This sort of specification is bad practice, because it is adding new
semantics to HTTP's status codes and methods, respectively; a semantics to HTTP's status codes and methods, respectively; a
recipient - whether it's an origin server, client library, recipient - whether it's an origin server, client library,
intermediary or cache - now has to know these extra semantics to intermediary or cache - now has to know these extra semantics to
understand the message. understand the message.
Some applications even require specific behaviours, such as: Some applications even require specific behaviours, such as:
A `POST` request MUST result in a `201 Created` response. A `POST` request MUST result in a `201 Created` response.
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but also in header fields. but also in header fields.
This allows a HTTP message to be examined by generic HTTP software This allows a HTTP message to be examined by generic HTTP software
(e.g., HTTP servers, intermediaries, client implementations), and its (e.g., HTTP servers, intermediaries, client implementations), and its
handling to be correctly determined. It also allows people to handling to be correctly determined. It also allows people to
leverage their knowledge of HTTP semantics without special-casing leverage their knowledge of HTTP semantics without special-casing
them for a particular application. them for a particular application.
Therefore, applications that use HTTP MUST NOT re-define, refine or Therefore, applications that use HTTP MUST NOT re-define, refine or
overlay the semantics of defined protocol elements. Instead, they overlay the semantics of defined protocol elements. Instead, they
SHOULD focus their specifications on protocol elements that are should focus their specifications on protocol elements that are
specific to that application; namely their HTTP resources. specific to that application; namely their HTTP resources.
See Section 4.2 for details. See Section 4.2 for details.
3.2. Links 3.2. Links
Another common practice is assuming that the HTTP server's name space Another common practice is assuming that the HTTP server's name space
(or a portion thereof) is exclusively for the use of a single (or a portion thereof) is exclusively for the use of a single
application. This effectively overlays special, application-specific application. This effectively overlays special, application-specific
semantics onto that space, precludes other applications from using semantics onto that space, precludes other applications from using
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RECOMMENDED that applications using HTTP define links in payloads, to RECOMMENDED that applications using HTTP define links in payloads, to
allow flexibility in deployment. allow flexibility in deployment.
Using runtime links in this fashion has a number of other benefits. Using runtime links in this fashion has a number of other benefits.
For example, navigating with a link allows a request to be routed to For example, navigating with a link allows a request to be routed to
a different server without the overhead of a redirection, thereby a different server without the overhead of a redirection, thereby
supporting deployment across machines well. It becomes possible to supporting deployment across machines well. It becomes possible to
"mix" different applications on the same server, and offers a natural "mix" different applications on the same server, and offers a natural
path for extensibility, versioning and capability management. path for extensibility, versioning and capability management.
3.3. Getting Value from HTTP 3.3. Rich Functionality
The simplest possible use of HTTP is to POST data to a single URL, The simplest possible use of HTTP is to POST data to a single URL,
thereby effectively tunnelling through the protocol. thereby effectively tunnelling through the protocol.
This "RPC" style of communication does get some benefit from using This "RPC" style of communication does get some benefit from using
HTTP - namely, message framing and the availability of HTTP - namely, message framing and the availability of
implementations - but fails to realise many others when used implementations - but fails to realise many others when used
exclusively: exclusively:
o Caching for server scalability, latency and bandwidth reduction, o Caching for server scalability, latency and bandwidth reduction,
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elements. elements.
4.1. Specifying the Use of HTTP 4.1. Specifying the Use of HTTP
When specifying the use of HTTP, an application SHOULD use [RFC7230] When specifying the use of HTTP, an application SHOULD use [RFC7230]
as the primary reference; it is not necessary to reference all of the as the primary reference; it is not necessary to reference all of the
specifications in the HTTP suite unless there are specific reasons to specifications in the HTTP suite unless there are specific reasons to
do so (e.g., a particular feature is called out). do so (e.g., a particular feature is called out).
Applications using HTTP MAY specify a minimum version to be supported Applications using HTTP MAY specify a minimum version to be supported
(HTTP/1.1 is suggested), and MUST NOT specify a maximum version. (HTTP/1.1 is suggested), and MUST NOT specify a maximum version, to
preserve the protocol's ability to evolve.
Likewise, applications need not specify what HTTP mechanisms - such Likewise, applications need not specify what HTTP mechanisms - such
as redirection, caching, authentication, proxy authentication, and so as redirection, caching, authentication, proxy authentication, and so
on - are to be supported. Full featured support for HTTP SHOULD be on - are to be supported. For example, an application can specify
taken for granted in servers and clients, and the application's that it uses HTTP like this:
function SHOULD degrade gracefully if they are not (although this
might be achieved by informing the user that their task cannot be
completed).
For example, an application can specify that it uses HTTP like this:
Foo Application uses HTTP {{RFC7230}}. Implementations MUST support Foo Application uses HTTP [RFC7230]. Implementations MUST support
HTTP/1.1, and MAY support later versions. Support for common HTTP HTTP/1.1, and MAY support later versions.
mechanisms such as redirection and caching are assumed.
When specifying examples of protocol interactions, applications When specifying examples of protocol interactions, applications
SHOULD document both the request and response messages, with full SHOULD document both the request and response messages, with full
headers, preferably in HTTP/1.1 format. For example: headers, preferably in HTTP/1.1 format. For example:
GET /thing HTTP/1.1 GET /thing HTTP/1.1
Host: example.com Host: example.com
Accept: application/things+json Accept: application/things+json
User-Agent: Foo/1.0 User-Agent: Foo/1.0
HTTP/1.1 200 OK HTTP/1.1 200 OK
Content-Type: application/things+json Content-Type: application/things+json
Content-Length: 500 Content-Length: 500
Server: Bar/2.2 Server: Bar/2.2
[payload here] [payload here]
4.2. Defining HTTP Resources 4.2. Defining HTTP Resources
HTTP Applications SHOULD focus on defining the following application- Applications that use HTTP should focus on defining the following
specific protocol elements: application-specific protocol elements:
o Media types [RFC6838], often based upon a format convention such o Media types [RFC6838], often based upon a format convention such
as JSON [RFC7159], as JSON [RFC8259],
o HTTP header fields, as per Section 4.7, and o HTTP header fields, as per Section 4.7, and
o The behaviour of resources, as identified by link relations o The behaviour of resources, as identified by link relations
[RFC5988]. [RFC8288].
By composing these protocol elements, an application can define a set By composing these protocol elements, an application can define a set
of resources, identified by link relations, that implement specified of resources, identified by link relations, that implement specified
behaviours, including: behaviours, including:
o Retrieval of their state using GET, in one or more formats o Retrieval of their state using GET, in one or more formats
identified by media type; identified by media type;
o Resource creation or update using POST or PUT, with an o Resource creation or update using POST or PUT, with an
appropriately identified request body format; appropriately identified request body format;
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For example, an application might specify: For example, an application might specify:
Resources linked to with the "example-widget" link relation type are Resources linked to with the "example-widget" link relation type are
Widgets. The state of a Widget can be fetched in the Widgets. The state of a Widget can be fetched in the
"application/example-widget+json" format, and can be updated by PUT "application/example-widget+json" format, and can be updated by PUT
to the same link. Widget resources can be deleted. to the same link. Widget resources can be deleted.
The "Example-Count" response header field on Widget representations The "Example-Count" response header field on Widget representations
indicates how many Widgets are held by the sender. indicates how many Widgets are held by the sender.
The "application/example-widget+json" format is a JSON {{RFC7159}} The "application/example-widget+json" format is a JSON [RFC8259]
format representing the state of a Widget. It contains links to format representing the state of a Widget. It contains links to
related information in the link indicated by the Link header field related information in the link indicated by the Link header field
value with the "example-other-info" link relation type. value with the "example-other-info" link relation type.
4.3. Specifying Client Behaviours 4.3. Specifying Client Behaviours
HTTP does not mandate some behaviours that have nevertheless become HTTP does not mandate some behaviours that have nevertheless become
very common; if these are not explicitly specified by applications very common; if these are not explicitly specified by applications
using HTTP, there may be confusing or interoperability problems. using HTTP, there may be confusion and interoperability problems.
This section lists common examples of this, and recommends default This section recommends default handling for these mechanisms.
handling for them.
o Redirect handling - applications using HTTP SHOULD specify that o Redirect handling - applications using HTTP SHOULD specify that
3xx redirect status codes be followed automatically. See 3xx redirect status codes be followed automatically. See
[RFC7231], Section 6.4. [RFC7231], Section 6.4.
o Redirect methods - applications using HTTP SHOULD specify that 301 o Redirect methods - applications using HTTP SHOULD specify that 301
and 302 redirect status codes rewrite the POST method to GET. See and 302 redirect status codes rewrite the POST method to GET. See
[RFC7231], Section 6.4. [RFC7231], Section 6.4.
o Cookies - Applications using HTTP MUST explicitly reference the o Cookies - Applications using HTTP MUST explicitly reference the
Cookie specification [RFC6265] if they are required. Cookie specification [RFC6265] if they are required.
o Certificates - Applications using HTTP MUST specify that TLS o Certificates - Applications using HTTP MUST specify that TLS
certificates are to be checked according to [RFC2818] when HTTPS certificates are to be checked according to [RFC2818] when HTTPS
is used. is used.
In general, applications using HTTP SHOULD align their usage as In general, applications using HTTP ought to align their usage as
closely as possible with Web browsers, to avoid interoperability closely as possible with Web browsers, to avoid interoperability
issues when they are used. See Section 4.10. issues when they are used. See Section 4.12.
If an application using HTTP has browser compatibility as a goal,
client interaction ought to be defined in terms of [FETCH], since
that is the abstraction that browsers use for HTTP; it enforces many
of these best practices.
Applications using HTTP MUST NOT require HTTP features that are Applications using HTTP MUST NOT require HTTP features that are
usually negotiated to be supported. For example, requiring that usually negotiated to be supported. For example, requiring that
clients support responses with a certain content-encoding ([RFC7231], clients support responses with a certain content-encoding ([RFC7231],
Section 3.1.2.2) instead of negotiating for it ([RFC7231], Section 3.1.2.2) instead of negotiating for it ([RFC7231],
Section 5.3.4) means that otherwise conformant clients cannot Section 5.3.4) means that otherwise conformant clients cannot
interoperate with the application. Applications MAY encourage the interoperate with the application. Applications MAY encourage the
implementation of such features, though. implementation of such features, though.
4.4. HTTP URLs 4.4. HTTP URLs
In HTTP, URLs are opaque identifiers under the control of the server. In HTTP, URLs are opaque identifiers under the control of the server.
As outlined in [RFC7320], standards cannot usurp this space, since it As outlined in [RFC7320], standards cannot usurp this space, since it
might conflict with existing resources, and constrain implementation might conflict with existing resources, and constrain implementation
and deployment. and deployment.
In other words, applications that use HTTP MUST NOT associate In other words, applications that use HTTP shouldn't associate
application semantics with specific URL paths on arbitrary servers. application semantics with specific URL paths on arbitrary servers.
Doing so inappropriately conflates the identity of the resource (its Doing so inappropriately conflates the identity of the resource (its
URL) with the capabilities that resource supports, bringing about URL) with the capabilities that resource supports, bringing about
many of the same interoperability problems that [RFC4367] warns of. many of the same interoperability problems that [RFC4367] warns of.
For example, specifying that a "GET to the URL /foo retrieves a bar For example, specifying that a "GET to the URL /foo retrieves a bar
document" is bad practice. Likewise, specifying "The widget API is document" is bad practice. Likewise, specifying "The widget API is
at the path /bar" violates [RFC7320]. at the path /bar" violates [RFC7320].
Instead, applications that use HTTP are encouraged to ensure that Instead, applications that use HTTP are encouraged to ensure that
URLs are discovered at runtime, allowing HTTP-based services to URLs are discovered at runtime, allowing HTTP-based services to
describe their own capabilities. One way to do this is to use typed describe their own capabilities. One way to do this is to use typed
links [RFC5988] to convey the URIs that are in use, as well as the links [RFC8288] to convey the URIs that are in use, as well as the
semantics of the resources that they identify. See Section 4.2 for semantics of the resources that they identify. See Section 4.2 for
details. details.
4.4.1. Initial URL Discovery 4.4.1. Initial URL Discovery
Generally, a client will begin interacting with a given application Generally, a client will begin interacting with a given application
server by requesting an initial document that contains information server by requesting an initial document that contains information
about that particular deployment, potentially including links to about that particular deployment, potentially including links to
other relevant resources. other relevant resources.
Applications that use HTTP SHOULD allow an arbitrary URL to be used Applications that use HTTP are encouraged to allow an arbitrary URL
as that entry point. For example, rather than specifying "the to be used as that entry point. For example, rather than specifying
initial document is at "/foo/v1", they should allow a deployment to "the initial document is at "/foo/v1", they should allow a deployment
use any URL as the entry point for the application. to use any URL as the entry point for the application.
In cases where doing so is impractical (e.g., it is not possible to In cases where doing so is impractical (e.g., it is not possible to
convey a whole URL, but only a hostname) standard applications that convey a whole URL, but only a hostname) standard applications that
use HTTP can request a well-known URL [RFC5785] as an entry point. use HTTP can request a well-known URL [RFC5785] as an entry point.
4.4.2. URL Schemes 4.4.2. URL Schemes
Applications that use HTTP will typically use the "http" and/or Applications that use HTTP will typically employ the "http" and/or
"https" URL schemes. "https" is preferred to provide authentication, "https" URL schemes. "https" is preferred to provide authentication,
integrity and confidentiality, as well as mitigate pervasive integrity and confidentiality, as well as mitigate pervasive
monitoring attacks [RFC7258]. monitoring attacks [RFC7258].
However, application-specific schemes can be defined as well. However, application-specific schemes can be defined as well.
When defining an URL scheme for an application using HTTP, there are When defining an URL scheme for an application using HTTP, there are
a number of tradeoffs and caveats to keep in mind: a number of tradeoffs and caveats to keep in mind:
o Unmodified Web browsers will not support the new scheme. While it o Unmodified Web browsers will not support the new scheme. While it
is possible to register new URL schemes with Web browsers (e.g. is possible to register new URL schemes with Web browsers (e.g.
registerProtocolHandler() in [HTML5] Section 8.7.1.3, as well as registerProtocolHandler() in [HTML5], as well as several
several proprietary approaches), support for these mechanisms is proprietary approaches), support for these mechanisms is not
not shared by all browsers, and their capabilities vary. shared by all browsers, and their capabilities vary.
o Existing non-browser clients, intermediaries, servers and o Existing non-browser clients, intermediaries, servers and
associated software will not recognise the new scheme. For associated software will not recognise the new scheme. For
example, a client library might fail to dispatch the request; a example, a client library might fail to dispatch the request; a
cache might refuse to store the response, and a proxy might fail cache might refuse to store the response, and a proxy might fail
to forward the request. to forward the request.
o Because URLs occur in and are generated in HTTP artefacts o Because URLs occur in and are generated in HTTP artefacts
commonly, often without human intervention (e.g., in the commonly, often without human intervention (e.g., in the
"Location" response header), it can be difficult to assure that "Location" response header), it can be difficult to assure that
skipping to change at page 11, line 44 skipping to change at page 12, line 16
o Features that rely upon the URL's origin [RFC6454], such as the o Features that rely upon the URL's origin [RFC6454], such as the
Web's same-origin policy, will be impacted by a change of scheme. Web's same-origin policy, will be impacted by a change of scheme.
o HTTP-specific features such as cookies [RFC6265], authentication o HTTP-specific features such as cookies [RFC6265], authentication
[RFC7235], caching [RFC7234], and CORS [FETCH] might or might not [RFC7235], caching [RFC7234], and CORS [FETCH] might or might not
work correctly, depending on how they are defined and implemented. work correctly, depending on how they are defined and implemented.
Generally, they are designed and implemented with an assumption Generally, they are designed and implemented with an assumption
that the URL will always be "http" or "https". that the URL will always be "http" or "https".
o Web features that require a secure context o Web features that require a secure context [SECCTXT] will likely
[W3C.CR-secure-contexts-20160915] will likely treat a new scheme treat a new scheme as insecure.
as insecure.
See [RFC7595] for more information about minting new URL schemes. See [RFC7595] for more information about minting new URL schemes.
4.4.3. Transport Ports 4.4.3. Transport Ports
Applications that use HTTP can use the applicable default port (80 Applications that use HTTP can use the applicable default port (80
for HTTP, 443 for HTTPS), or they can be deployed upon other ports. for HTTP, 443 for HTTPS), or they can be deployed upon other ports.
This decision can be made at deployment time, or might be encouraged This decision can be made at deployment time, or might be encouraged
by the application's specification (e.g., by registering a port for by the application's specification (e.g., by registering a port for
that application). that application).
In either case, non-default ports will need to be reflected in the In either case, non-default ports will need to be reflected in the
authority of all URLs for that resource; the only mechanism for authority of all URLs for that resource; the only mechanism for
changing a default port is changing the scheme (see Section 4.4.2). changing a default port is changing the scheme (see Section 4.4.2).
Using a port other than the default has privacy implications (i.e., Using a port other than the default has privacy implications (i.e.,
the protocol can now be distinguished from other traffic), as well as the protocol can now be distinguished from other traffic), as well as
operability concerns (as some networks might block or otherwise operability concerns (as some networks might block or otherwise
interfere with it). Privacy implications SHOULD be documented in interfere with it). Privacy implications should be documented in
Security Considerations. Security Considerations.
See [RFC7605] for further guidance. See [RFC7605] for further guidance.
4.5. HTTP Methods 4.5. HTTP Methods
Applications that use HTTP MUST confine themselves to using Applications that use HTTP MUST confine themselves to using
registered HTTP methods such as GET, POST, PUT, DELETE, and PATCH. registered HTTP methods such as GET, POST, PUT, DELETE, and PATCH.
New HTTP methods are rare; they are required to be registered with New HTTP methods are rare; they are required to be registered with
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resources, not just those of one application. resources, not just those of one application.
While historically some applications (e.g., [RFC4791]) have defined While historically some applications (e.g., [RFC4791]) have defined
non-generic methods, [RFC7231] now forbids this. non-generic methods, [RFC7231] now forbids this.
When authors believe that a new method is required, they are When authors believe that a new method is required, they are
encouraged to engage with the HTTP community early, and document encouraged to engage with the HTTP community early, and document
their proposal as a separate HTTP extension, rather than as part of their proposal as a separate HTTP extension, rather than as part of
an application's specification. an application's specification.
4.5.1. GET
GET is one of the most common and useful HTTP methods; its retrieval
semantics allow caching, side-effect free linking and forms the basis
of many of the benefits of using HTTP.
A common use of GET is to perform queries, often using the query
component of the URL; this is this a familiar pattern from Web
browsing, and the results can be cached, improving efficiency of an
often expensive process.
In some cases, however, GET might be unwieldy for expressing queries,
because of the limited syntax of the URL; in particular, if binary
data forms part of the query terms, it needs to be encoded to conform
to URL syntax.
While this is not an issue for short queries, it can become one for
larger query terms, or ones which need to sustain a high rate of
requests. Additionally, some HTTP implementations limit the size of
URLs they support - although modern HTTP software has much more
generous limits than previously (typically, considerably more than
8000 octets, as required by [RFC7230] Section 3.1.1).
In these cases, an application using HTTP might consider using POST
to express queries in the request body; doing so avoids encoding
overhead and URL length limits in implementations. However, in doing
so it should be noted that the benefits of GET such as caching and
linking to query results are lost. Therefore, applications using
HTTP that feel a need to allow POST queries ought consider allowing
both methods.
Applications that use HTTP SHOULD NOT define GET requests to have
side effects, since implementations can and do retry HTTP GET
requests that fail.
Finally, note that while HTTP allows GET requests to have a body
syntactically, this is done only to allow parsers to be generic; as
per [RFC7231], Section 4.3.1, a body on a GET has no meaning, and
will be either ignored or rejected by generic HTTP software. As a
result, applications that use HTTP SHOULD NOT define GET to have any
sde effects upon their resources.
4.6. HTTP Status Codes 4.6. HTTP Status Codes
Applications that use HTTP MUST only use registered HTTP status Applications that use HTTP MUST only use registered HTTP status
codes. codes.
As with methods, new HTTP status codes are rare, and required (by As with methods, new HTTP status codes are rare, and required (by
[RFC7231]) to be registered with IETF review. Similarly, HTTP status [RFC7231]) to be registered with IETF review. Similarly, HTTP status
codes are generic; they are required (by [RFC7231]) to be potentially codes are generic; they are required (by [RFC7231]) to be potentially
applicable to all resources, not just to those of one application. applicable to all resources, not just to those of one application.
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Furthermore, applications using HTTP MUST NOT re-specify the Furthermore, applications using HTTP MUST NOT re-specify the
semantics of HTTP status codes, even if it is only by copying their semantics of HTTP status codes, even if it is only by copying their
definition. They MUST NOT require specific reason phrases to be definition. They MUST NOT require specific reason phrases to be
used; the reason phrase has no function in HTTP, and is not used; the reason phrase has no function in HTTP, and is not
guaranteed to be preserved by implementations. The reason phrase is guaranteed to be preserved by implementations. The reason phrase is
not carried in the [RFC7540] message format. not carried in the [RFC7540] message format.
Typically, applications using HTTP will convey application-specific Typically, applications using HTTP will convey application-specific
information in the message body and/or HTTP header fields, not the information in the message body and/or HTTP header fields, not the
status code. status code. [RFC7807] provides one way for applications using HTTP
to do this.
Specifications sometimes also create a "laundry list" of potential Specifications sometimes also create a "laundry list" of potential
status codes, in an effort to be helpful. The problem with doing so status codes, in an effort to be helpful. The problem with doing so
is that such a list is never complete; for example, if a network is that such a list is never complete; for example, if a network
proxy is interposed, the client might encounter a "407 Proxy proxy is interposed, the client might encounter a "407 Proxy
Authentication Required" response; or, if the server is rate limiting Authentication Required" response; or, if the server is rate limiting
the client, it might receive a "429 Too Many Requests" response. the client, it might receive a "429 Too Many Requests" response.
Since the list of HTTP status codes can be added to, it's safer to Since the list of HTTP status codes can be added to, it's safer to
refer to it directly, and point out that clients SHOULD be able to specify behaviours in terms of general response classes (e.g.,
handle all applicable protocol elements gracefully (i.e., falling "successful response" for 2xx; "client error" for 4xx and "server
back to the generic "n00" semantics of a given status code; e.g., error" for 5xx), pointing out that clients SHOULD be able to handle
"499" can be safely handled as "400" by clients that don't recognise all applicable protocol elements gracefully (i.e., falling back to
it). the generic "n00" semantics of a given status code; e.g., "499" can
be safely handled as "400" by clients that don't recognise it).
4.7. HTTP Header Fields 4.7. HTTP Header Fields
Applications that use HTTP MAY define new HTTP header fields, Applications that use HTTP MAY define new HTTP header fields,
following the advice in [RFC7231], Section 8.3.1. following the advice in [RFC7231], Section 8.3.1.
Typically, using HTTP header fields is appropriate in a few different Typically, using HTTP header fields is appropriate in a few different
situations: situations:
o Their content is useful to intermediaries (who often wish to avoid o Their content is useful to intermediaries (who often wish to avoid
parsing the body), and/or parsing the body), and/or
o Their content is useful to generic HTTP software (e.g., clients, o Their content is useful to generic HTTP software (e.g., clients,
servers), and/or servers), and/or
o It is not possible to include their content in the message body o It is not possible to include their content in the message body
(usually because a format does not allow it). (usually because a format does not allow it).
If none of these motivations apply, using a header field is NOT
RECOMMENDED.
New header fields MUST be registered, as per [RFC7231] and [RFC3864]. New header fields MUST be registered, as per [RFC7231] and [RFC3864].
It is RECOMMENDED that header field names be short (even when HTTP/2 It is RECOMMENDED that header field names be short (even when HTTP/2
header compression is in effect, there is an overhead) but header compression is in effect, there is an overhead) but
appropriately specific. In particular, if a header field is specific appropriately specific. In particular, if a header field is specific
to an application, an identifier for that application SHOULD form a to an application, an identifier for that application SHOULD form a
prefix to the header field name, separated by a "-". prefix to the header field name, separated by a "-".
For example, if the "example" application needs to create three For example, if the "example" application needs to create three
headers, they might be called "example-foo", "example-bar" and headers, they might be called "example-foo", "example-bar" and
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consuming more generic header names, not to reserve a portion of the consuming more generic header names, not to reserve a portion of the
namespace for the application; see [RFC6648] for related namespace for the application; see [RFC6648] for related
considerations. considerations.
The semantics of existing HTTP header fields MUST NOT be re-defined The semantics of existing HTTP header fields MUST NOT be re-defined
without updating their registration or defining an extension to them without updating their registration or defining an extension to them
(if allowed). For example, an application using HTTP cannot specify (if allowed). For example, an application using HTTP cannot specify
that the "Location" header has a special meaning in a certain that the "Location" header has a special meaning in a certain
context. context.
If an application defines a request header field that might be used See Section 4.9 for the interaction between headers and HTTP caching;
by a server to change the response's headers or body, authors should in particular, request headers that are used to "select" a response
point out that this has implications for caching; in general, such have impact there, and need to be carefully considered.
resources need to either make their responses uncacheable (e.g., with
the "no-store" cache-control directive defined in [RFC7234],
Section 5.2.2.3) or consistently send the Vary response header
([RFC7231], Section 7.1.4).
See Section 4.9 for requirements regarding header fields that carry
application state (e.g,. Cookie).
Applications that use already-defined HTTP header fields MUST NOT See Section 4.10 for considerations regarding header fields that
modify their semantics or syntax, unless the definition of that carry application state (e.g,. Cookie).
header field explicitly allows it (e.g., with an extension field).
4.8. Defining Message Payloads 4.8. Defining Message Payloads
There are many potential formats for payloads; for example, JSON There are many potential formats for payloads; for example, JSON
[RFC8259], XML [W3C.REC-xml-20081126], and CBOR [RFC7049]. Best [RFC8259], XML [XML], and CBOR [RFC7049]. Best practices for their
practices for their use are out of scope for this document. use are out of scope for this document.
Applications SHOULD register distinct media types for each format Applications SHOULD register distinct media types for each format
they define; this makes it possible to identify them unambiguously they define; this makes it possible to identify them unambiguously
and negotiate for their use. See [RFC6838] for more information. and negotiate for their use. See [RFC6838] for more information.
4.9. Authentication and Application State 4.9. HTTP Caching
HTTP caching [RFC7234] is one of the primary benefits of using HTTP
for applications; it provides scalability, reduces latency and
improves reliability. Furthermore, HTTP caches are readily available
in browsers and other clients, networks as forward and reverse
proxies, Content Delivery Networks and as part of server software.
Assigning even a short freshness lifetime ([RFC7234], Section 4.2) -
e.g., 5 seconds - allows a response to be reused to satisfy multiple
clients, and/or a single client making the same request repeatedly.
In general, if it is safe to reuse something, consider assigning a
freshness lifetime; cache implementations take active measures to
expire content intelligently when they are out of space, so "it will
fill up the cache" is not a valid concern.
Understand that stale responses (e.g., one with "Cache-Control: max-
age=0") can be reused when the cache is disconnected from the origin
server; this can be useful for handling network issues. See
[RFC7234], Section 4.2.4, and also [RFC5861] for additional controls
over stale content.
Stale responses can be refreshed by assigning a validator, saving
both transfer bandwidth and latency for large responses; see
[RFC7232].
In some situations, responses without explicit cache directives
(e.g., Cache-Control or Expires) will be stored and served using a
heuristic freshness lifetime; see [RFC7234], Section 4.2.2. As the
heuristic is not under control of the application, it is generally
preferable to set an explicit freshness lifetime.
If caching of a response is not desired, the appropriate response
directive is "Cache-Control: no-store". This only need be sent in
situations where the response might be cached; see [RFC7234],
Section 3.
If an application defines a request header field that might be used
by a server to change the response's headers or body, authors should
point out that this has implications for caching; in general, such
resources need to either make their responses uncacheable (e.g., with
the "no-store" cache-control directive defined in [RFC7234],
Section 5.2.2.3) or consistently send the Vary response header
([RFC7231], Section 7.1.4).
When an application has a need to express a lifetime that's separate
from the freshness lifetime, this should be expressed separately,
either in the response's body or in a separate header field. When
this happens, the relationship between HTTP caching and that lifetime
need to be carefully considered, since the response will be used as
long as it is considered fresh.
Like other functions, HTTP caching is generic; it does not have
knowledge of the application in use. Therefore, caching extensions
need to be backwards-compatible, as per [RFC7234], Section 5.2.3.
4.10. Application State
Applications that use HTTP MAY use stateful cookies [RFC6265] to Applications that use HTTP MAY use stateful cookies [RFC6265] to
identify a client and/or store client-specific data to contextualise identify a client and/or store client-specific data to contextualise
requests. requests.
If it is only necessary to identify clients, applications that use When used, it is important to carefully specify the scoping and use
HTTP MAY use HTTP authentication [RFC7235]. If the Basic of cookies; if the application exposes sensitive data or capabilities
authentication scheme [RFC7617] is used, it MUST NOT be used with the (e.g., by acting as an ambient authority), exploits are possible.
'http' URL scheme. If the Digest scheme [RFC7616] is used, it MUST Mitigations include using a request-specific token to assure the
NOT be used with the 'http' URL scheme, unless the chosen hash intent of the client.
algorithm is not "MD5".
In either case, it is important to carefully specify the scoping and
use of these mechanisms; if they expose sensitive data or
capabilities (e.g., by acting as an ambient authority), exploits are
possible. Mitigations include using a request-specific token to
assure the intent of the client.
Applications MUST NOT make assumptions about the relationship between Applications MUST NOT make assumptions about the relationship between
separate requests on a single transport connection; doing so breaks separate requests on a single transport connection; doing so breaks
many of the assumptions of HTTP as a stateless protocol, and will many of the assumptions of HTTP as a stateless protocol, and will
cause problems in interoperability, security, operability and cause problems in interoperability, security, operability and
evolution. evolution.
4.10. Co-Existing with Web Browsing 4.11. Client Authentication
Applications that use HTTP MAY use HTTP authentication [RFC7235] to
identify clients. The Basic authentication scheme [RFC7617] MUST NOT
be used unless the underlying transport is authenticated, integrity-
protected and confidential (e.g., as provided the "HTTPS" URL scheme,
or another using TLS). The Digest scheme [RFC7616] MUST NOT be used
unless the underlying transport is similarly secure, or the chosen
hash algorithm is not "MD5".
When used, it is important to carefully specify the scoping and use
of authentication; if the application exposes sensitive data or
capabilities (e.g., by acting as an ambient authority), exploits are
possible. Mitigations include using a request-specific token to
assure the intent of the client.
4.12. Co-Existing with Web Browsing
Even if there is not an intent for an application that uses HTTP to Even if there is not an intent for an application that uses HTTP to
be used with a Web browser, its resources will remain available to be used with a Web browser, its resources will remain available to
browsers and other HTTP clients. browsers and other HTTP clients.
This means that all such applications need to consider how browsers This means that all such applications need to consider how browsers
will interact with them, particularly regarding security. will interact with them, particularly regarding security.
For example, if an application's state can be changed using a POST For example, if an application's state can be changed using a POST
request, a Web browser can easily be coaxed into making that request request, a Web browser can easily be coaxed into making that request
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Or, if a resource reflects data from the request into a response, Or, if a resource reflects data from the request into a response,
that can be used to perform a Cross-Site Scripting attack on Web that can be used to perform a Cross-Site Scripting attack on Web
browsers directed to it. browsers directed to it.
This is only a small sample of the kinds of issues that applications This is only a small sample of the kinds of issues that applications
using HTTP must consider. Generally, the best approach is to using HTTP must consider. Generally, the best approach is to
consider the application _as_ a Web application, and to follow best consider the application _as_ a Web application, and to follow best
practices for their secure development. practices for their secure development.
A complete enumeration of such practices is out of scope for this A complete enumeration of such practices is out of scope for this
document. External resources are numerous; e.g., document, but some considerations include:
https://www.owasp.org/index.php/OWASP_Guide_Project [4].
4.11. Co-Existing with Other Applications o Using Strict Transport Security [RFC6797] to assure that HTTPS is
used
o Using Content-Security-Policy [W3C.WD-CSP3-20160913] to constrain
the capabilities of content, thereby mitigating Cross-Site
Scripting attacks (which are possible if client-provided data is
exposed in any part of a response in the application)
o Using X-Frame-Options [RFC7034] to prevent content from being
included in a HTML frame from another origin, thereby enabling
"clickjacking"
o Using Referrer-Policy [W3C.CR-referrer-policy-20170126] to prevent
sensitive data in URLs from being leaked in the Referer request
header
o Using the 'HttpOnly' flag on Cookies to assure that cookies are
not exposed to browser scripting languages [RFC6265]
Depending on how they are intended to be deployed, specifications for
applications using HTTP might require the use of these mechanisms in
specific ways, or might merely point them out in Security
Considerations.
If an application using HTTP has browser compatibility as a goal,
client interaction ought to be defined in terms of [FETCH], since
that is the abstraction that browsers use for HTTP; it enforces many
of these best practices.
4.13. Application Boundaries
Because the origin [RFC6454] is how many HTTP capabilities are Because the origin [RFC6454] is how many HTTP capabilities are
scoped, applications also need to consider how deployments might scoped, applications also need to consider how deployments might
interact with other applications (including Web browsing) on the same interact with other applications (including Web browsing) on the same
origin. origin.
For example, if Cookies [RFC6265] are used to carry application For example, if Cookies [RFC6265] are used to carry application
state, they will be sent with all requests to the origin by default, state, they will be sent with all requests to the origin by default,
unless scoped by path, and the application might receive cookies from unless scoped by path, and the application might receive cookies from
other applications on the origin. This can lead to security issues, other applications on the origin. This can lead to security issues,
as well as collisions in cookie name. as well as collision in cookie names.
As a result, when specifying the use of Cookies, HTTP authentication One solution to these issues is to require a dedicated hostname for
[RFC7235], or other origin-wide HTTP mechanisms, applications using the application, so that it has a unique origin. However, it is
HTTP SHOULD NOT mandate the use of a particular identifier, but often desirable to allow multiple applications to be deployed on a
instead let deployments configure them. single hostname; doing so provides the most deployment flexibility
and enables them to be "mixed" together (See [RFC7320] for details).
Therefore, applications using HTTP should strive to allow multiple
applications on an origin.
Note that dedicating a hostname to a single application is not a To enable this, when specifying the use of Cookies, HTTP
solution to the issues above; see [RFC7320]. authentication realms [RFC7235], or other origin-wide HTTP
mechanisms, applications using HTTP SHOULD NOT mandate the use of a
particular identifier, but instead let deployments configure them.
Consideration SHOULD be given to scoping them to part of the origin,
using their specified mechanisms for doing so.
Modern Web browsers constrain the ability of content from one origin Modern Web browsers constrain the ability of content from one origin
to access resources from another, to avoid the "confused deputy" to access resources from another, to avoid leaking private
problem. As a result, applications that wish to expose cross-origin information. As a result, applications that wish to expose cross-
data to browsers will need to implement [W3C.REC-cors-20140116]. origin data to browsers will need to implement the CORS protocol; see
[FETCH].
5. IANA Considerations 5. IANA Considerations
This document has no requirements for IANA. This document has no requirements for IANA.
6. Security Considerations 6. Security Considerations
Section 4.9 discusses the impact of using stateful mechanisms in the Section 4.10 discusses the impact of using stateful mechanisms in the
protocol as ambient authority, and suggests a mitigation. protocol as ambient authority, and suggests a mitigation.
Section 4.4.2 requires support for 'https' URLs, and discourages the Section 4.4.2 requires support for 'https' URLs, and discourages the
use of 'http' URLs, to provide authentication, integrity and use of 'http' URLs, to provide authentication, integrity and
confidentiality, as well as mitigate pervasive monitoring attacks. confidentiality, as well as mitigate pervasive monitoring attacks.
Section 4.10 highlights the implications of Web browsers' Section 4.12 highlights the implications of Web browsers'
capabilities on applications that use HTTP. capabilities on applications that use HTTP.
Section 4.11 discusses the issues that arise when applications are Section 4.13 discusses the issues that arise when applications are
deployed on the same origin as Web sites (and other applications). deployed on the same origin as Web sites (and other applications).
Applications that use HTTP in a manner that involves modification of Applications that use HTTP in a manner that involves modification of
implementations - for example, requiring support for a new URL implementations - for example, requiring support for a new URL
scheme, or a non-standard method - risk having those implementations scheme, or a non-standard method - risk having those implementations
"fork" from their parent HTTP implementations, with the possible "fork" from their parent HTTP implementations, with the possible
result that they do not benefit from patches and other security result that they do not benefit from patches and other security
improvements incorporated upstream. improvements incorporated upstream.
7. References 7. References
skipping to change at page 17, line 40 skipping to change at page 21, line 5
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000, DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>. <https://www.rfc-editor.org/info/rfc2818>.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004, DOI 10.17487/RFC3864, September 2004,
<https://www.rfc-editor.org/info/rfc3864>. <https://www.rfc-editor.org/info/rfc3864>.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010,
<https://www.rfc-editor.org/info/rfc5988>.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, [RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011, DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/info/rfc6454>. <https://www.rfc-editor.org/info/rfc6454>.
[RFC6648] Saint-Andre, P., Crocker, D., and M. Nottingham, [RFC6648] Saint-Andre, P., Crocker, D., and M. Nottingham,
"Deprecating the "X-" Prefix and Similar Constructs in "Deprecating the "X-" Prefix and Similar Constructs in
Application Protocols", BCP 178, RFC 6648, Application Protocols", BCP 178, RFC 6648,
DOI 10.17487/RFC6648, June 2012, DOI 10.17487/RFC6648, June 2012,
<https://www.rfc-editor.org/info/rfc6648>. <https://www.rfc-editor.org/info/rfc6648>.
skipping to change at page 19, line 9 skipping to change at page 22, line 23
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540, Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015, DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>. <https://www.rfc-editor.org/info/rfc7540>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[W3C.REC-cors-20140116] [RFC8288] Nottingham, M., "Web Linking", RFC 8288,
Kesteren, A., "Cross-Origin Resource Sharing", World Wide DOI 10.17487/RFC8288, October 2017,
Web Consortium Recommendation REC-cors-20140116, January <https://www.rfc-editor.org/info/rfc8288>.
2014, <http://www.w3.org/TR/2014/REC-cors-20140116>.
7.2. Informative References 7.2. Informative References
[FETCH] WHATWG, "Fetch - Living Standard", n.d., [FETCH] WHATWG, "Fetch - Living Standard", n.d.,
<https://fetch.spec.whatwg.org>. <https://fetch.spec.whatwg.org>.
[HTML5] WHATWG, "HTML - Living Standard", n.d., [HTML5] WHATWG, "HTML - Living Standard", n.d.,
<https://html.spec.whatwg.org>. <https://html.spec.whatwg.org>.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
skipping to change at page 19, line 38 skipping to change at page 23, line 5
1983, <https://www.rfc-editor.org/info/rfc854>. 1983, <https://www.rfc-editor.org/info/rfc854>.
[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol", [RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985, STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985,
<https://www.rfc-editor.org/info/rfc959>. <https://www.rfc-editor.org/info/rfc959>.
[RFC2821] Klensin, J., Ed., "Simple Mail Transfer Protocol", [RFC2821] Klensin, J., Ed., "Simple Mail Transfer Protocol",
RFC 2821, DOI 10.17487/RFC2821, April 2001, RFC 2821, DOI 10.17487/RFC2821, April 2001,
<https://www.rfc-editor.org/info/rfc2821>. <https://www.rfc-editor.org/info/rfc2821>.
[RFC3205] Moore, K., "On the use of HTTP as a Substrate", BCP 56,
RFC 3205, DOI 10.17487/RFC3205, February 2002,
<https://www.rfc-editor.org/info/rfc3205>.
[RFC4367] Rosenberg, J., Ed. and IAB, "What's in a Name: False [RFC4367] Rosenberg, J., Ed. and IAB, "What's in a Name: False
Assumptions about DNS Names", RFC 4367, Assumptions about DNS Names", RFC 4367,
DOI 10.17487/RFC4367, February 2006, DOI 10.17487/RFC4367, February 2006,
<https://www.rfc-editor.org/info/rfc4367>. <https://www.rfc-editor.org/info/rfc4367>.
[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault, [RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791, "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
DOI 10.17487/RFC4791, March 2007, DOI 10.17487/RFC4791, March 2007,
<https://www.rfc-editor.org/info/rfc4791>. <https://www.rfc-editor.org/info/rfc4791>.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785, Uniform Resource Identifiers (URIs)", RFC 5785,
DOI 10.17487/RFC5785, April 2010, DOI 10.17487/RFC5785, April 2010,
<https://www.rfc-editor.org/info/rfc5785>. <https://www.rfc-editor.org/info/rfc5785>.
[RFC5861] Nottingham, M., "HTTP Cache-Control Extensions for Stale
Content", RFC 5861, DOI 10.17487/RFC5861, May 2010,
<https://www.rfc-editor.org/info/rfc5861>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011, DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>. <https://www.rfc-editor.org/info/rfc6265>.
[RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol", [RFC6455] Fette, I. and A. Melnikov, "The WebSocket Protocol",
RFC 6455, DOI 10.17487/RFC6455, December 2011, RFC 6455, DOI 10.17487/RFC6455, December 2011,
<https://www.rfc-editor.org/info/rfc6455>. <https://www.rfc-editor.org/info/rfc6455>.
[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797,
DOI 10.17487/RFC6797, November 2012,
<https://www.rfc-editor.org/info/rfc6797>.
[RFC7034] Ross, D. and T. Gondrom, "HTTP Header Field X-Frame-
Options", RFC 7034, DOI 10.17487/RFC7034, October 2013,
<https://www.rfc-editor.org/info/rfc7034>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>. October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>. 2014, <https://www.rfc-editor.org/info/rfc7258>.
[RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines [RFC7595] Thaler, D., Ed., Hansen, T., and T. Hardie, "Guidelines
and Registration Procedures for URI Schemes", BCP 35, and Registration Procedures for URI Schemes", BCP 35,
RFC 7595, DOI 10.17487/RFC7595, June 2015, RFC 7595, DOI 10.17487/RFC7595, June 2015,
<https://www.rfc-editor.org/info/rfc7595>. <https://www.rfc-editor.org/info/rfc7595>.
[RFC7605] Touch, J., "Recommendations on Using Assigned Transport [RFC7605] Touch, J., "Recommendations on Using Assigned Transport
skipping to change at page 20, line 43 skipping to change at page 24, line 23
[RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP [RFC7616] Shekh-Yusef, R., Ed., Ahrens, D., and S. Bremer, "HTTP
Digest Access Authentication", RFC 7616, Digest Access Authentication", RFC 7616,
DOI 10.17487/RFC7616, September 2015, DOI 10.17487/RFC7616, September 2015,
<https://www.rfc-editor.org/info/rfc7616>. <https://www.rfc-editor.org/info/rfc7616>.
[RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme", [RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme",
RFC 7617, DOI 10.17487/RFC7617, September 2015, RFC 7617, DOI 10.17487/RFC7617, September 2015,
<https://www.rfc-editor.org/info/rfc7617>. <https://www.rfc-editor.org/info/rfc7617>.
[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
<https://www.rfc-editor.org/info/rfc7807>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259, Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017, DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/info/rfc8259>. <https://www.rfc-editor.org/info/rfc8259>.
[W3C.CR-secure-contexts-20160915] [SECCTXT] West, M., "Secure Contexts", World Wide Web Consortium CR
West, M., "Secure Contexts", World Wide Web Consortium CR
CR-secure-contexts-20160915, September 2016, CR-secure-contexts-20160915, September 2016,
<https://www.w3.org/TR/2016/CR-secure-contexts-20160915>. <https://www.w3.org/TR/2016/CR-secure-contexts-20160915>.
[W3C.REC-xml-20081126] [W3C.CR-referrer-policy-20170126]
Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and Eisinger, J. and E. Stark, "Referrer Policy", World Wide
Web Consortium CR CR-referrer-policy-20170126, January
2017,
<https://www.w3.org/TR/2017/CR-referrer-policy-20170126>.
[W3C.WD-CSP3-20160913]
West, M., "Content Security Policy Level 3", World Wide
Web Consortium WD WD-CSP3-20160913, September 2016,
<https://www.w3.org/TR/2016/WD-CSP3-20160913>.
[XML] Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
Edition)", World Wide Web Consortium Recommendation REC- Edition)", World Wide Web Consortium Recommendation REC-
xml-20081126, November 2008, xml-20081126, November 2008,
<http://www.w3.org/TR/2008/REC-xml-20081126>. <http://www.w3.org/TR/2008/REC-xml-20081126>.
7.3. URIs 7.3. URIs
[1] https://lists.w3.org/Archives/Public/ietf-http-wg/ [1] https://lists.w3.org/Archives/Public/ietf-http-wg/
[2] http://httpwg.github.io/ [2] http://httpwg.github.io/
[3] https://github.com/httpwg/http-extensions/labels/bcp56bis [3] https://github.com/httpwg/http-extensions/labels/bcp56bis
[4] https://www.owasp.org/index.php/OWASP_Guide_Project Appendix A. Changes from RFC 3205
Appendix A. Changes from RFC3205
RFC3205 captured the Best Current Practice in the early 2000's, based [RFC3205] captured the Best Current Practice in the early 2000's,
on the concerns facing protocol designers at the time. Use of HTTP based on the concerns facing protocol designers at the time. Use of
has changed considerably since then, and as a result this document is HTTP has changed considerably since then, and as a result this
substantially different. As a result, the changes are too numerous document is substantially different. As a result, the changes are
to list individually. too numerous to list individually.
Author's Address Author's Address
Mark Nottingham Mark Nottingham
Email: mnot@mnot.net Email: mnot@mnot.net
URI: https://www.mnot.net/ URI: https://www.mnot.net/
 End of changes. 61 change blocks. 
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