fix(Authenticator): Handling expired sessions

[sebaland]

Issue #, if available:

• Authenticator does not refresh identity pool credentials #86

Description of changes:

When a user session cannot be refreshed, Amplify.Auth.fetchAuthSession() will still return isSignedIn: true, but attempting to perform any operation that requires authentication will subsequently fail and ask the user to log in again.

This is a known thing within Amplify, but can be handled by the Authenticator by signing out the user if we detect their session has expired when the component is launched.

This PR proposes validating that a session has valid identity ID and/or Cognito tokens, depending on what type of configuration the user is using:

• If they only have CognitoIdentity, only check for a valid `session.getIdentityId()
• If they only have CognitoUserPool, only check for valid session.getCognitoTokens().
• If they have both, check for both session.getIdentityId() and session.getCognitoTokens().

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[codecov]

Codecov Report

Attention: Patch coverage is 11.42857% with 31 lines in your changes missing coverage. Please review.

Project coverage is 41.69%. Comparing base (2518b16) to head (1f05357).
Report is 1 commits behind head on main.

Files	Patch %	Lines
...rces/Authenticator/Models/AuthenticatorState.swift	0.00%	20 Missing ⚠️
...enticator/Configuration/AmplifyConfiguration.swift	26.66%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
- Coverage   42.20%   41.69%   -0.51%     
==========================================
  Files          41       41              
  Lines        1872     1902      +30     
==========================================
+ Hits          790      793       +3     
- Misses       1082     1109      +27     

Flag	Coverage Δ
Authenticator	41.69% <11.42%> (-0.51%)	⬇️

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