gRFC L74: Java Channel Credentials

[Eric Anderson]

This is a thread to discuss https://github.com/grpc/proposal/pull/198

It is an enhancement for Java to add ChannelCredentials and ServerCredentials. This brings Java closer to C and Go (but stronger to C than Go with the composite creds). We've been avoiding this for years as it is quite a bit of work to design and it has never been quite important enough. But things have slowly progressed to impacting more users and "custom" credentials are becoming more common.

Make special note how constructing ManagedChannelBuilders works, as it is currently proposing a small but important change compared to the current flow.

[Eric Anderson]

We settled on using Grpc.newChannelBuilder() and Grpc.newChannelBuilderForAddress() for the new location of the builder construction methods.

But there's been discussion about how to construct credentials. The current proposal has things like GoogleDefaultChannelCredentials which don't actually extend ChannelCredentials and so do not have constructors (only have factory methods). We're choosing how to deal with this. See my comment on the subject.