signIn method should provide using audience prop in userData

[maxism]

Changes

According to the documentation we can use audience property in API call to specify identifier of the API we are trying to use. So in this PR the prop has been added to the documentation and tests.

References

Please include relevant links supporting this change such as a:

• https://auth0.com/docs/api/authentication?http#get-code-or-link

Testing

• This change adds unit test coverage
• This change adds integration test coverage

Checklist

• I have read the Auth0 general contribution guidelines
• I have read the Auth0 Code of Conduct
• All existing and new tests complete without errors

[adamjmcgrath]

Thanks @maxism