Update CredentialManager classes to include IDToken expiration

[lbalmaceda]

Changes

Made both classes aware of the ID Token exp value (when available) to decide when the whole Credentials object can be renewed.

References

Closes #253

Testing

Added more unit tests

• This change adds unit test coverage

• [] This change adds integration test coverage

• This change has been tested on the latest version of the platform/language or why not

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

[stevehobbsdev]

@lbalmaceda Having a test suite for JWTDecoder seems redundant to me. The decoder doesn't do anything except wrap com.auth0.android.jwt.JWT (and I assume that library is also tested - if not, these tests should live there).

The fact that the credentials manager classes make use of the decoded token should be enough to provide coverage and assurance that the decoder class is working as intended. What do you think?

[lbalmaceda]

@stevehobbsdev

Having a test suite for JWTDecoder seems redundant to me

The JWT library we use has its own tests, true.. However, because there's a token decoding step inside the process of "saving a token in the manager", I need to be able to test when that step fails or succeeds, given different scenarios. So I'm opening the constructor (package-privately) so that the test classes can see it and use that other signature that receives a "JWT decoder" instance for my tests to mock it.

But since my tests are mocking it, I cannot ensure that the "JWT decoding" step does actually what it is supposed to do: decode a real JWT string into a JWT instance. So I'm adding a simple test for that JWTDecoder package-private class in which I don't mock anything but I assert a token string gets decoded into a real JWT class here.

Say I change this line and I make it return a decoded JWT for a different hardcoded token, and don't make use of the one received as param. If I wouldn't be testing the JWTDecoder class then I wouldn't caught that error.

[lbalmaceda]

Will release this next week. 🏁