Exact Federation `Authorization` header format isn't clear

[ShadowJonathan]

Link to problem area

https://matrix.org/docs/spec/server_server/r0.1.4#request-authentication

Issue

Came up in #conduit:fachschaften.org; It's not clear that the parameters after X-Matrix can use quotes or not, RFC2184 was mentioned with the following quote:

Note that quotes around parameter values are part of the value
syntax; they are NOT part of the value itself. Furthermore, it is
explicitly permitted to have a mixture of quoted and unquoted
continuation fields.

Maybe this clarification can be added as an informational footnote.

[tulir]

Maybe this clarification can be added as an informational footnote.

The clarification should probably be made the spec, and the example can be moved to an informational footnote

[uhoreg]

The format for the Authorization header is actually in RFC2735, and almost matches what is done in Matrix. The approach that I've taken in #1067 is to say that we follow RFC2735, but if you want to be nice to servers, follow these more restricted rules.