Google Vertex AI not working with gRPC transport

[KushParsaniya]

Issue with grpc Transport in Spring Boot Configuration

I am facing an issue when using the grpc transport for the spring.ai.vertex.ai.gemini configuration in my Spring Boot application. The error occurs as follows:

io.grpc.StatusRuntimeException: UNAUTHENTICATED: Request had invalid authentication credentials. Expected OAuth 2 access token, login cookie or other valid authentication credential. See https://developers.google.com/identity/sign-in/web/devconsole-project.
    at io.grpc.Status.asRuntimeException(Status.java:533) ~[grpc-api-1.62.2.jar:1.62.2]
    at io.grpc.stub.ClientCalls$UnaryStreamToFuture.onClose(ClientCalls.java:538) ~[grpc-stub-1.62.2.jar:1.62.2]
    at io.grpc.PartialForwardingClientCallListener.onClose(PartialForwardingClientCallListener.java:39) ~[grpc-api-1.62.2.jar:1.62.2]
    at io.grpc.ForwardingClientCallListener.onClose(ForwardingClientCallListener.java:23) ~[grpc-api-1.62.2.jar:1.62.2]

This error is encountered with the following configuration:

spring.ai.vertex.ai.gemini.project-id=${PROJECT_ID}
spring.ai.vertex.ai.gemini.location=${PROJECT_ZONE}
spring.ai.vertex.ai.gemini.credentials-uri=${API_KEY}
spring.ai.vertex.ai.gemini.transport=grpc  # Default config

However, when I switch to using the rest transport, the configuration works fine without any authentication errors:

spring.ai.vertex.ai.gemini.project-id=${PROJECT_ID}
spring.ai.vertex.ai.gemini.location=${PROJECT_ZONE}
spring.ai.vertex.ai.gemini.credentials-uri=${API_KEY}
spring.ai.vertex.ai.gemini.transport=rest  # change to rest

Question:

Is there a specific reason why the grpc transport is resulting in authentication errors? Are there additional steps or configurations needed to use grpc with OAuth 2 credentials in this context?