add comments for Oauth interface

[yxxhero]

Description

Related Issue

Motivation and Context

Screenshots (if appropriate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 34.41%. Comparing base (6b60929) to head (93a2dd3).
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4038      +/-   ##
==========================================
+ Coverage   34.39%   34.41%   +0.01%     
==========================================
  Files         343      343              
  Lines       40211    40211              
==========================================
+ Hits        13832    13839       +7     
+ Misses      25463    25457       -6     
+ Partials      916      915       -1     

Flag	Coverage Δ
unittests	34.41% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
manager/auth/oauth/oauth.go	0.00% <ø> (ø)

... and 6 files with indirect coverage changes

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[chlins]

lgtm

[gaius-qi]

LGTM