BUG/MINOR: http-fetch: check against the whole token in get_http_auth()

BUG/MINOR: http-fetch: check against the whole token in get_http_auth()

In 1.4, Basic authentication support was added by commit f9423ae43a
("[MINOR] acl: add http_auth and http_auth_group"). Interestingly,
a mistake there consisted in taking the length of the comparison from
the input token, so "b" matches "Basic". It was later propagated to
Bearer in 2.5 with commit f5dd337b12 ("MINOR: http:
Add http_auth_bearer sample fetch"). Let's just compare the entire
tokens.

This may be backported though it is very minor.