User Names for HTTP Resources
draft-vanrein-http-unauth-user-02

Abstract

Most protocols support users under domain names, but HTTP does not. Usage patterns in the wild do suggest a desire to have this facility. This specification defines a header for user names, orthogonal to any authentication or authorisation concerns.

Status of This Memo

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This Internet-Draft will expire on July 27, 2020.

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Table of Contents

• 1. Introduction
• 2. The HTTP User Header
• 3. Protocol Handling of HTTP User
• 4. Caching Behaviour
• 5. IANA Considerations
• 6. Security Considerations
• 7. Normative References
• Appendix A. HTTP User Environment Variable
• Author's Address

1. Introduction

Most protocols support Network Access Identifiers [RFC7542] like john@example.com to identify users like john under domains such as example.com. The URI format for HTTP can express [Section 2.7.1 of [RFC7230]] such authority sections, and many online applications seem to want to address individual users, but HTTP URIs do not usually express user names. This specification therefore introduces a header "User", in close parallel to the "Host" header.

Historically, user names have been coupled to (Basic and Digest) authentication. This is not generally correct; the user name in the URI indicates a resource name space, not an (authenticating) visitor. By using a new header field, this specification allows authentication to be orthogonal to resource name space selection.

Some user agents have supported (Basic and Digest) authentication with a "user:password" format in the authority section of URIs. This has now been deprecated [Section 3.2.1 of [RFC3986]] but the form with just "user" and no ":password" continues to be acceptable. Various HTTP clients have different handling for this form, sometimes flagging it incorrectly as a security hazard, which also motivates a specification for proper handling.

TODO: Issue filed with HTTPbis, https://github.com/httpwg/http-core/issues/278 and offered a Pull Request, https://github.com/httpwg/http-core/compare/master...arpa2:userinfo-password as a followup of somewhat late Errata against RFC7230, https://www.rfc-editor.org/errata/eid5964

The purpose of this specification is to define clear meaning for HTTP URIs with a user name.

2. The HTTP User Header

The "User" header field provides an aspect of the desired resource name scope. The value is usually taken from the authority section [Section 3.2 of [RFC3986]] of the target URI and MUST NOT include a ":" colon (U+003a) character.

User = 1*( unreserved / pct-encoded / sub-delims )

The User header value holds precisely one value with the following ABNF grammar: [RFC3986]. Zeal in the use of the "pct-encoded" non-terminal for plain characters that have a direct representation MAY be treated as an attempted attack.

The User header MAY appear in requests and MUST NOT occur in responses. When unrecognised by HTTP servers, the User header is ignored [Section 3.2.1 of [RFC7230]]. Intermediates such as proxies and caches MUST NOT add, remove or modify the User header.

3. Protocol Handling of HTTP User

User agents SHOULD render user names in authority sections whenever they render host names, though it may be helpful if it stands out graphically [Section 7.6 of [RFC3986]]. User agents SHOULD NOT remove user names from the target URI. User agents MAY remove the "@" (U+0040) symbol from a URI when the preceding user name is empty. User agents MUST refuse URIs with a ":" colon (U+003a) in the user name but MUST NOT complain about a user name that does not have that character.

During redirects or other traversals to (relative) HTTP URIs, the user name MUST be overwritten when the new URI specifies an authority component, and it MUST be kept otherwise.

4. Caching Behaviour

The privacy or security of an HTTP resource is not impacted by the use of a User header. This is because User is about resource location, but not about client identity.

HTTP caches [RFC7234] need to distinguish requests with different User header values. The Vary header [Section 7.1.4 of [RFC7231]] MUST be present in the matching response, and the header MUST either be a single "*" star (U+002a) or list the "user" name, for all responses whose processing was influenced by the User header. This requirement does not apply to software and configurations that ignore the User header.

5. IANA Considerations

Header Field Name   Template   Protocol   Status    Reference
------------------  ---------  ---------  -------   ----------
User                           http       TBD       TBD:THIS_SPEC

IANA adds the following entry to the Message Headers registry:

6. Security Considerations

The User header field as defined herein is orthogonal to issues of authentication or authorisation, and adds no security concerns.

7. Normative References

Appendix A. HTTP User Environment Variable

The following variable SHOULD be passed up to applications on a HTTP server:

HTTP_USER

gives the HTTP User header value after parsing and percent-decoding. Like the customary variables HTTP_HOST and PATH_INFO, this specifies the resource being requested. The HTTP_USER header does not describe the identity of the HTTP client.

Author's Address