Allow Credentials in POST

[danygielow]

client_id and client_secret can also be given via POST data. So added client_id and client_secret to Post namedtuple and trying to retrieve them via POST first. Auth Header if they were not found.

https://www.oauth.com/oauth2-servers/access-tokens/client-credentials/

[aliev]

@danygielow thank you for another great PR! I will take a look this evening, we have small issues in typing: https://github.com/aliev/aioauth/pull/24/checks?check_run_id=2001875113

/home/runner/work/aioauth/aioauth/src/aioauth/grant_type.py
  47:32 - error: Argument of type "str | None" cannot be assigned to parameter "client_id" of type "str" in function "get_client"
    Type "str | None" cannot be assigned to type "str"
      Type "None" cannot be assigned to type "str" (reportGeneralTypeIssues)
1 error, 0 warnings, 0 infos 
Completed in 1.629sec

[synchronizing]

Seems good with me.

Note on RFC6749 Section 3.2, Token Endpoint:

The client MUST use the HTTP "POST" method when making access token requests.

[codecov-io]

Codecov Report

Merging #24 (4049f5a) into master (0d790df) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #24      +/-   ##
==========================================
+ Coverage   99.26%   99.27%   +0.01%     
==========================================
  Files          15       15              
  Lines         541      549       +8     
  Branches       55       56       +1     
==========================================
+ Hits          537      545       +8     
  Misses          3        3              
  Partials        1        1              

Impacted Files	Coverage Δ
src/aioauth/grant_type.py	100.00% <100.00%> (ø)
src/aioauth/requests.py	100.00% <100.00%> (ø)

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[synchronizing]

All seems resolved. @aliev Everything looks good to me. 👍🏼

[aliev]

for me looks great as well :) @danygielow great job thank you! approved