bug#57956: 29.0.50; Add minimal authorization support to sasl-scram-rfc

[J.P.]

Tags: patch

Hi people,

ERC plans on basing its SASL library on sasl.el and friends. Although
rare, authorization (or "authz") support is sometimes needed by IRC
administrators wanting to authenticate as other users. It's also
expected by at least one IRC-compliance test suite [1]. The PLAIN
implementation in sasl.el currently offers implicit support via the
`authenticator-name' client property (see `sasl-plain-response'). This
patch proposes we do much the same with sasl-scram-rfc.el.

As for specifics, I've encapsulated the actual prop-lookup and
header-construction details in a new function that's called indirectly
via a new top-level variable (although perhaps that's just unnecessary
or more suited to a user option). The only other change appears in
`sasl-scram--client-final-message'. It concerns the base64 encoding of
the GS2 header and the client proof, both of which currently suffer from
occasional whitespace complications [2].

Anyway, ERC would benefit greatly from these (or superior) changes
because we'd like to introduce `erc-compat' analogs in an upcoming
release (probably ERC 5.6). If anyone out there can spare the time,
your feedback would be greatly appreciated.

Thanks,
J.P.

P.S. Tests covering these changes appear in the patch sets for bug#29108
and bug#49860.


[1] Authz support for PLAIN, with SCRAM possibly on the way:

    https://github.com/progval/irctest/blob/master/irctest/client_tests/sasl.py

[2] Calling `base64-encode-string' with NO-LINE-BREAK set to t seems to
    solve the issue, which is likely related to this excerpt from
    https://www.rfc-editor.org/rfc/rfc5802#section-2.1:
 
     "The use of base64 in SCRAM is restricted to the canonical form
      with no whitespace."
 
    FWIW, I tried advising `base64-encode-string' to avoid having to
    submit a patch, but it seems the byte compiler precomputes the
    result for certain constant params, like `cbind-input' in
    `sasl-scram--client-final-message'.


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0001-Add-GS2-authorization-to-sasl-scram-rfc.patch
Description: Text Data