add server side verification documentation to authenticateUserWithGoogle

[dlandtaa]

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Documentation changes
• Other... Please describe:

PR Checklist

Please check your PR fulfills the following requirements:

Bugfixes:

• Regression testing has been carried out using the example project to ensure the intended bug is fixed and no regression bugs have been inadvertently introduced.

New features/enhancements:

• Exhaustive testing has been carried out for the new functionality
• Regression testing has been carried out to ensure no existing functionality is adversely affected
• Documentation has been added / updated
• The example project has been update to validate/demonstrate the new functionality.

What is the purpose of this PR?

Update to documentation related to server side validation of id token returned by authenticateUserWithGoogle().

Does this PR introduce a breaking change?

• Yes
• No

What testing has been done on the changes in the PR?

n/a

What testing has been done on existing functionality?

n/a

Other information