User Names for HTTP Resources
draft-vanrein-http-unauth-user-03

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 29, 2020.

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Table of Contents

• 1. Introduction
• 2. The HTTP User Header
• 3. Protocol Handling of HTTP User
• 4. Orthogonality of Authentication (Example)
• 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 specifies a resource name space, not an (authenticated) client identity. 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.

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] and can be directly included in the quoted-string form; a plain token cannot express "(", ")", "=", ";" and "," without escaping [Section 3.2.6 of [RFC7230]].

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 reject userinfo sections containing a colon ":" (U+003a) or URI syntax errors and MAY warn about potential security problems when they contain a dot "." (U+002e), but SHOULD accept and pass all other non-empty userinfo sections that conform to URI syntax in a User header.

The User header MAY appear in requests and MUST NOT occur in responses. When sending it, the user agent SHOULD generate User as the next header field after Host. Transparent intermediates such as proxies and caches MUST NOT add, remove or modify the User header. The CONNECT method and Host header both exclude this information, and the User header completes it.

Servers MAY ignore the User header [Section 3.2.1 of [RFC7230]]. When they use it, the Effective Request URI [Section 5.5 of [RFC7230]] is constructed with the userinfo and the at "@" delimiter (U+0040) prefixed to the host name and optional port. Although authentication is orthogonal to resource selection, the scope of a realm is scoped under the authority section [Section 2.2 of [RFC7235]] and so the userinfo partitions realms.

HTTP caches [RFC7234] derive no privacy or security concerns from the User header, but they do need to to differentiate requests based on it. To accommodate that, the Vary header [Section 7.1.4 of [RFC7231]] MUST be generated by the server 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 has no bearing on server software and configurations that ignore the User header.

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. User agents MUST refuse URIs with non-empty userinfo sub-component that do not conform to the User header grammar; user agents MUST send any other non-empty userinfo sub-components as the value of the User header in requests for the target URI.

4. Orthogonality of Authentication (Example)

The user name in a URI refines the resource selection process on a host, but it is easily confused with the orthogonal concept of authentication. Below is an example to demonstrate how these concepts relate intuitively, but only as the result of access control, which is a local choice on the server but not a specification-driven connection. By demonstrating group access, the example shows a less restrictive model that derives from this orthogonality of concepts.

The remainder of this section is informative.

GET /docs HTTP/1.1
Host: example.com
User: sales

HTTP/1.1 301 Moved Permanently
Location: /docs/
Vary: User

GET /docs/ HTTP/1.1
Host: example.com
User: sales

HTTP/1.1 401 Unauthorized
WWW-Authenticate: Knock realm="Documents"
Vary: User

GET /docs/ HTTP/1.1
Host: example.com
User: sales
Authorization: Knock realm="Documents", user="mary", ...

HTTP/1.1 200 OK
Vary: User
Content-Type: text/html

...
<a href="/docs/review.cgi?docid=123">Review 123 now</a>
...

GET /docs/review.cgi?docid=123 HTTP/1.1
Host: example.com
User: sales
Authorization: Knock realm="Documents", user="mary", ...

John and Mary both work at the Sales department of Example, Inc. John has written a document and wants Mary to review it. Mary opens a link to the document name space under the sales account at https://sales@example.com/docs and her user agent sends:

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 that run on top of the HTTP stack in a server:

LOCAL_USER

gives the HTTP User header value after grammar checking 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, which usually lands in REMOTE_USER after authentication.

Author's Address