Need to ensure we use lower-case gRPC header keys

[omaray]

This might be a no-op, but please double check. Filing this issue just in case.

We need to ensure that all headers used for gRPC are written in lower-case. Please review this Pull Request for reference of what needs to be updated.

Again, perhaps this doesn't apply to your language. Feel free to comment and close the issue (after you double checking).

[mziccard]

We don't explicitly set any gRPC header. @garrettjonesgoogle do you?

[garrettjonesgoogle]

Our code doesn't have any uppercase text that it puts in the header. We should probably do a more thorough audit of the headers that are passed.

[jgeewax]

Not even user-agent ?

[mziccard]

We set the user agent via a call to GAX, not setting the header key directly. I logged the headers of a request to PubSub and the user-agent related headers look fine, keys are: user-agent and x-google-apis-agent.

[omaray]

Can the issue be closed?