feat: HTTP Bearer Authorization for simple use cases

[robbat2]

Add support for HTTP Bearer Authorization for simple use cases, where HTTP Basic might not fit workflows.

Signed-off-by: Robin H. Johnson robbat2@gentoo.org

[SuperQ]

I wonder if we should support arbitrary headers, rather than specifically one kind of bearer token. The reason we have the basic auth here is because there's some standard encoding involved. Authorization: Bearer xxxx is a simple opaque string.

[robbat2]

I actually started considering other auth to add, including HTTP Digest (which also needs special handling like Basic)

For your proposal, it would be match header to accept:

match_header:
  authorization:
    - "Bearer foo"
    - "FakeAuth value2"
  x-random-stuff:
    - "abc123"

[SuperQ]

Some work on Digest auth was being done over in the common package.

prometheus/common#553

[robbat2]

@SuperQ hmm, reading that, I realize there is more auth support in common already that not being exposed in toolkit; should I include that in this PR?