updated GetRequestingParty APIs to support Basic client authentication

[ghost]

Solution for #323

All GetRequestingParty APIs can now be used using Basic authorization header (clientID and clientSecret), or as previous using Bearer authorization header (token).
The basic authentication is useful for being able to request the evaluation of a user token (provided into SubjectToken) using a service account.

[Nerzal]

Hi, can you please fetch the changes from the main branch into your branch? That should fix the error in the test :)

[ghost]

Hi, I have just updated the PR branch from main branch

[codecov]

Codecov Report

Merging #324 (3676e52) into main (44f36fb) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #324      +/-   ##
==========================================
+ Coverage   76.60%   76.66%   +0.05%     
==========================================
  Files           4        4              
  Lines        1962     1967       +5     
==========================================
+ Hits         1503     1508       +5     
  Misses        319      319              
  Partials      140      140              

Impacted Files	Coverage Δ
client.go	74.87% <100.00%> (+0.07%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 44f36fb...3676e52. Read the comment docs.

[Nerzal]

My review comments won't save due to some bug.

So here it is again:

If the clientSecret is only needed, when checking basic auth stuff.
Can we somehow make this optional?

The API gets harder to use, as the consumer of the API might not know when the clientSecret can be empty and when it needs to be filled.