Background

In #14733, we added a public option ApiKeyOption. On second thought, we think we would rather have a credentials factory function:

std::shared_ptr<Credentials> MakeApiKeyCredentials(std::string api_key, Options o = {});

This disallows configurations where ApiKeyOption and UnifiedCredentialsOption are set simultaneously (which is good, because the configuration is invalid).

Work

We need to:

• Update the sample to use other types (GrpcCredentialOption + CustomMetadataOption) than ApiKeyOption.
  • The existing sample is already published to cloud docs.
  • I do not want to remove it. That would be annoying.
• Remove ApiKeyOption and all code downstream of it. Almost none of this is salvageable.
  • After this, we can say the release is unblocked.
• Expand oauth2_internal::Credentials to allow for API keys.
  • This might look like a std::string ApiKey()
  • or it might look like a StatusOr<std::pair<std::string, std::string>> AuthHeader()
• Add an ApiKeyConfig credential type and do a lot of plumbing.
  • Unified gRPC credentials
  • Unified REST credentials
• Add MakeApiKeyCredentials(...)