alts: Introduce AltsContext to allow outside packages accessing ALTS information

[martin-schaub]

No description provided.

[ejona86]

Is this for testing this class or for letting other classes testing themselves?

[martin-schaub]

This should make classes that use the AltsContext testable. However, without parameters this isn't very useful. Therefore I've changed the method to specify the service accounts (security level is fixed anyway).

[ejona86]

While security level is fixed today, you can't actually test any code that looks at it if it is hard-coded during testing. It seems like maybe we should just suck it up and make a builder fascade as well, that delegates to HandshakerResult's builder. @jiangtaoli2016, thoughts?

I'm actually fairly okay with this as it stands, if we do want to leave it as-is. We tend to limit VisibleForTesting usage to instances where the project's own unit tests need access. For cases like this, we'd just call this "a public API". Let's remove the VisibleForTesting annotation here? I honestly don't see much harm someone could do, even using it in production.

[jiangtaoli2016]

I am fine with it, since AltsContext is just a wrapper of AltsInternalContext. This fixed security level is only exposed for testing.

[martin-schaub]

I've removed the VisibleForTesting annotation.

[ejona86]

One comment that could be small or could be more, depending on how @jiangtaoli2016 feels about it as well.

[jiangtaoli2016]

Thanks for creating the AltsContext Wrapper.

[martin-schaub]

@ejona86 is there something missing or could you merge please?

[ejona86]

Oh, sorry. I had been waiting for the CI to finish and then failed to come back around to it.