Fix typo in IdentityProvider documentation

[danielyahn]

Previous section has the following description

The first step is "Authentication" (identifying who is making the request). This is handled by the :class:.IdentityProvider.

I think it's more correct to say IdentityProvider class is responsible for the "authentication" step, instead of "authorization"

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Codecov Report

Merging #915 (05ddb36) into main (3090893) will not change coverage.
The diff coverage is n/a.

❗ Current head 05ddb36 differs from pull request most recent head 6eca214. Consider uploading reports for the commit 6eca214 to get more accurate results

@@           Coverage Diff           @@
##             main     #915   +/-   ##
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  Coverage   72.24%   72.24%           
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  Files          65       65           
  Lines        7983     7983           
  Branches     1334     1334           
=======================================
  Hits         5767     5767           
  Misses       1810     1810           
  Partials      406      406           

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