draft-ietf-httpbis-bcp56bis-01.txt   draft-ietf-httpbis-bcp56bis-02.txt 
HTTP M. Nottingham HTTP M. Nottingham
Internet-Draft February 12, 2018 Internet-Draft February 28, 2018
Obsoletes: 3205 (if approved) Obsoletes: 3205 (if approved)
Intended status: Best Current Practice Intended status: Best Current Practice
Expires: August 16, 2018 Expires: September 1, 2018
On the use of HTTP as a Substrate On the use of HTTP as a Substrate
draft-ietf-httpbis-bcp56bis-01 draft-ietf-httpbis-bcp56bis-02
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.
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
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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 August 16, 2018. This Internet-Draft will expire on September 1, 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
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. Getting Value from HTTP . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . . 7
4.2. Defining HTTP Resources . . . . . . . . . . . . . . . . . 8 4.2. Defining HTTP Resources . . . . . . . . . . . . . . . . . 8
4.3. HTTP URLs . . . . . . . . . . . . . . . . . . . . . . . . 9 4.3. Specifying Client Behaviours . . . . . . . . . . . . . . 9
4.3.1. Initial URL Discovery . . . . . . . . . . . . . . . . 9 4.4. HTTP URLs . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3.2. URL Schemes . . . . . . . . . . . . . . . . . . . . . 10 4.4.1. Initial URL Discovery . . . . . . . . . . . . . . . . 10
4.3.3. Transport Ports . . . . . . . . . . . . . . . . . . . 11 4.4.2. URL Schemes . . . . . . . . . . . . . . . . . . . . . 10
4.4. HTTP Methods . . . . . . . . . . . . . . . . . . . . . . 11 4.4.3. Transport Ports . . . . . . . . . . . . . . . . . . . 12
4.5. HTTP Status Codes . . . . . . . . . . . . . . . . . . . . 12 4.5. HTTP Methods . . . . . . . . . . . . . . . . . . . . . . 12
4.6. HTTP Header Fields . . . . . . . . . . . . . . . . . . . 13 4.6. HTTP Status Codes . . . . . . . . . . . . . . . . . . . . 12
4.7. Defining Message Payloads . . . . . . . . . . . . . . . . 14 4.7. HTTP Header Fields . . . . . . . . . . . . . . . . . . . 13
4.8. Authentication and Application State . . . . . . . . . . 14 4.8. Defining Message Payloads . . . . . . . . . . . . . . . . 15
4.9. Co-Existing with Web Browsing . . . . . . . . . . . . . . 14 4.9. Authentication and Application State . . . . . . . . . . 15
4.10. Co-Existing with Other Applications . . . . . . . . . . . 15 4.10. Co-Existing with Web Browsing . . . . . . . . . . . . . . 15
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 4.11. Co-Existing with Other Applications . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7.1. Normative References . . . . . . . . . . . . . . . . . . 16 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.2. Informative References . . . . . . . . . . . . . . . . . 18 7.1. Normative References . . . . . . . . . . . . . . . . . . 17
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 20 7.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Changes from RFC3205 . . . . . . . . . . . . . . . . 20 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 20 Appendix A. Changes from RFC3205 . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 21
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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document, we say an application is _using HTTP_ when any of the document, we say an application is _using HTTP_ when any of the
following conditions are true: following conditions are true:
o The transport port in use is 80 or 443, o The transport port in use is 80 or 443,
o The URL scheme "http" or "https" is used, o The URL scheme "http" or "https" is used,
o The ALPN protocol ID [RFC7301] generically identifies HTTP (e.g., o The ALPN protocol ID [RFC7301] generically identifies HTTP (e.g.,
"http/1.1", "h2", "h2c"), or "http/1.1", "h2", "h2c"), or
o The message formats described in [RFC7230] and/or [RFC7540] are o The IANA registries defined for HTTP are updated or modified.
used in conjunction with the IANA registries defined for HTTP.
When an application is using HTTP, all of the requirements of the When an application is using HTTP, all of the requirements of the
HTTP protocol suite (including but not limited to [RFC7230], HTTP protocol suite (including but not limited to [RFC7230],
[RFC7231], [RFC7232], [RFC7233], [RFC7234], [RFC7235] and [RFC7540]) [RFC7231], [RFC7232], [RFC7233], [RFC7234], [RFC7235] and [RFC7540])
are in force. are in force.
An application might not be _using HTTP_ according to this An application might not be _using HTTP_ according to this
definition, but still relying upon the HTTP specifications in some definition, but still relying upon the HTTP specifications in some
manner. For example, an application might wish to avoid re- manner. For example, an application might wish to avoid re-
specifying parts of the message format, but change others; or, it specifying parts of the message format, but change others; or, it
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"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. Getting Value from HTTP
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: implementations - but fails to realise many others when used
exclusively:
o Caching for server scalability, latency and bandwidth reduction, o Caching for server scalability, latency and bandwidth reduction,
and reliability; and reliability;
o Authentication and access control; o Granularity of access control (through use of a rich space of
URLs);
o Automatic redirection;
o Partial content to selectively request part of a response; o Partial content to selectively request part of a response;
o Natural support for extensions and versioning through protocol o Definition of an information space using URLs; and
extension; and
o The ability to interact with the application easily using a Web o The ability to interact with the application easily using a Web
browser. browser.
Using such a high-level protocol to tunnel simple semantics has Using such a high-level protocol to tunnel simple semantics has
downsides too; because of its more advanced capabilities, breadth of downsides too; because of its more advanced capabilities, breadth of
deployment and age, HTTP's complexity can cause interoperability deployment and age, HTTP's complexity can cause interoperability
problems that could be avoided by using a simpler substrate (e.g., problems that could be avoided by using a simpler substrate (e.g.,
WebSockets [RFC6455], if browser support is necessary, or TCP WebSockets [RFC6455], if browser support is necessary, or TCP
[RFC0793] if not), or making the application be _based upon HTTP_, [RFC0793] if not), or making the application be _based upon HTTP_,
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[payload here] [payload here]
4.2. Defining HTTP Resources 4.2. Defining HTTP Resources
HTTP Applications SHOULD focus on defining the following application- HTTP Applications SHOULD focus on defining the following application-
specific protocol elements: 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 [RFC7159],
o HTTP header fields, as per Section 4.6, 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]. [RFC5988].
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;
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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 {{RFC7159}}
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. HTTP URLs 4.3. Specifying Client Behaviours
HTTP does not mandate some behaviours that have nevertheless become
very common; if these are not explicitly specified by applications
using HTTP, there may be confusing or interoperability problems.
This section lists common examples of this, and recommends default
handling for them.
o Redirect handling - applications using HTTP SHOULD specify that
3xx redirect status codes be followed automatically. See
[RFC7231], Section 6.4.
o Redirect methods - applications using HTTP SHOULD specify that 301
and 302 redirect status codes rewrite the POST method to GET. See
[RFC7231], Section 6.4.
o Cookies - Applications using HTTP MUST explicitly reference the
Cookie specification [RFC6265] if they are required.
o Certificates - Applications using HTTP MUST specify that TLS
certificates are to be checked according to [RFC2818] when HTTPS
is used.
In general, applications using HTTP SHOULD align their usage as
closely as possible with Web browsers, to avoid interoperability
issues when they are used. See Section 4.10.
Applications using HTTP MUST NOT require HTTP features that are
usually negotiated to be supported. For example, requiring that
clients support responses with a certain content-encoding ([RFC7231],
Section 3.1.2.2) instead of negotiating for it ([RFC7231],
Section 5.3.4) means that otherwise conformant clients cannot
interoperate with the application. Applications MAY encourage the
implementation of such features, though.
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 MUST NOT 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
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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 [RFC5988] 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.
4.3.1. 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 SHOULD allow an arbitrary URL to be used
as that entry point. For example, rather than specifying "the as that entry point. For example, rather than specifying "the
initial document is at "/foo/v1", they should allow a deployment to initial document is at "/foo/v1", they should allow a deployment to
use any URL as the entry point for the application. 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.
4.3.2. URL Schemes 4.4.2. URL Schemes
Applications that use HTTP will typically use the "http" and/or Applications that use HTTP will typically use 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:
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which can present security and operability issues. For example, which can present security and operability issues. For example,
using a new scheme to assure that requests don't get sent to a using a new scheme to assure that requests don't get sent to a
"normal" Web site is likely to fail. "normal" Web site is likely to fail.
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
[W3C.CR-secure-contexts-20160915] will likely treat a new scheme [W3C.CR-secure-contexts-20160915] will likely 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.
4.3.3. 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 4.3.2). 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.
4.4. 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
IETF Review (see [RFC7232]), and are also required to be _generic_. IETF Review (see [RFC7232]), and are also required to be _generic_.
That means that they need to be potentially applicable to all That means that they need to be potentially applicable to all
resources, not just those of one application. resources, not just those of one application.
While historically some applications (e.g., [RFC4791]) has 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 it is believed that a new method is required, authors 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. 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.
When it is believed that a new status code is required, authors are When authors believe that a new status code 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.
Status codes' primary function is to convey HTTP semantics for the The primary function of status codes is to convey HTTP semantics for
benefit of generic HTTP software, not application-specific semantics. the benefit of generic HTTP software, not application-specific
Therefore, applications MUST NOT specify additional semantics or semantics. Therefore, applications MUST NOT specify additional
refine existing semantics for status codes. semantics or refine existing semantics for status codes.
In particular, specifying that a particular status code has a In particular, specifying that a particular status code has a
specific meaning in the context of an application is harmful, as specific meaning in the context of an application is harmful, as
these are not generic semantics, since the consumer needs to be in these are not generic semantics, since the consumer needs to be in
the context of the application to understand them. the context of the application to understand them.
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
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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 refer to it directly, and point out that clients SHOULD be able to
handle all applicable protocol elements gracefully (i.e., falling handle all applicable protocol elements gracefully (i.e., falling
back to the generic "n00" semantics of a given status code; e.g., back to the generic "n00" semantics of a given status code; e.g.,
"499" can be safely handled as "400" by clients that don't recognise "499" can be safely handled as "400" by clients that don't recognise
it). it).
4.6. 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
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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.
See Section 4.8 for requirements regarding header fields that carry 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).
See Section 4.9 for requirements regarding header fields that carry
application state (e.g,. Cookie). application state (e.g,. Cookie).
4.7. Defining Message Payloads Applications that use already-defined HTTP header fields MUST NOT
modify their semantics or syntax, unless the definition of that
header field explicitly allows it (e.g., with an extension field).
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] and XML [W3C.REC-xml-20081126]. Best practices for their [RFC8259], XML [W3C.REC-xml-20081126], and CBOR [RFC7049]. Best
use are out of scope for this document. practices for their 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.
4.8. Authentication and Application State 4.9. Authentication and 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 If it is only necessary to identify clients, applications that use
HTTP MAY use HTTP authentication [RFC7235]; if either of the Basic HTTP MAY use HTTP authentication [RFC7235]. If the Basic
[RFC7617] or Digest [RFC7616] authentication schemes is used, it MUST authentication scheme [RFC7617] is used, it MUST NOT be used with the
NOT be used with the 'http' URL scheme. 'http' URL scheme. If the Digest scheme [RFC7616] is used, it MUST
NOT be used with the 'http' URL scheme, unless the chosen hash
algorithm is not "MD5".
In either case, it is important to carefully specify the scoping and In either case, it is important to carefully specify the scoping and
use of these mechanisms; if they expose sensitive data or use of these mechanisms; if they expose sensitive data or
capabilities (e.g., by acting as an ambient authority), exploits are capabilities (e.g., by acting as an ambient authority), exploits are
possible. Mitigations include using a request-specific token to possible. Mitigations include using a request-specific token to
assure the intent of the client. 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.
4.9. Co-Existing with Web Browsing 4.10. 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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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. External resources are numerous; e.g.,
https://www.owasp.org/index.php/OWASP_Guide_Project [4]. https://www.owasp.org/index.php/OWASP_Guide_Project [4].
4.10. Co-Existing with Other Applications 4.11. Co-Existing with Other Applications
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,
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to access resources from another, to avoid the "confused deputy" to access resources from another, to avoid the "confused deputy"
problem. As a result, applications that wish to expose cross-origin problem. As a result, applications that wish to expose cross-origin
data to browsers will need to implement [W3C.REC-cors-20140116]. data to browsers will need to implement [W3C.REC-cors-20140116].
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 4.8 discusses the impact of using stateful mechanisms in the Section 4.9 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 4.3.2 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 4.9 highlights the implications of Web browsers' capabilities Section 4.10 highlights the implications of Web browsers'
on applications that use HTTP. capabilities on applications that use HTTP.
Section 4.11 discusses the issues that arise when applications are
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
7.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<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, [RFC5988] Nottingham, M., "Web Linking", RFC 5988,
DOI 10.17487/RFC5988, October 2010, DOI 10.17487/RFC5988, October 2010,
<https://www.rfc-editor.org/info/rfc5988>. <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,
skipping to change at page 19, line 9 skipping to change at page 20, line 13
<https://www.rfc-editor.org/info/rfc5785>. <https://www.rfc-editor.org/info/rfc5785>.
[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>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <https://www.rfc-editor.org/info/rfc7049>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <https://www.rfc-editor.org/info/rfc7159>. 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,
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