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How does gRPC support interceptors for cross-cutting concerns like authentication, logging, and retries, similar to middleware in a REST pipeline?

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Answer

gRPC interceptors (implementing Interceptor, either server-side or client-side) wrap around RPC calls, letting you inject logic before and after the actual call executes -- server-side interceptors handle concerns like authentication/authorization and logging uniformly across all gRPC methods, while client-side interceptors handle concerns like automatic retry logic, adding auth headers, or client-side logging/metrics, registered globally so individual service methods don't need to repeat this logic.

public class LoggingInterceptor : Interceptor {
    public override async Task<TResponse> UnaryServerHandler<TRequest, TResponse>(
        TRequest request, ServerCallContext context, UnaryServerMethod<TRequest, TResponse> continuation) {
        _logger.LogInformation("Calling {Method}", context.Method);
        return await continuation(request, context);
    }
}

builder.Services.AddGrpc(options => options.Interceptors.Add<LoggingInterceptor>());

Real-world example A microservices platform registers a global server-side interceptor validating a JWT token on every incoming gRPC call, ensuring consistent authentication enforcement across dozens of gRPC service methods without duplicating auth-checking code in each one.

Common follow-ups: How do interceptors compare conceptually to ASP.NET Core middleware for REST APIs?;How do you chain multiple interceptors and control their execution order?

ASP.NET Core Middleware & Request Pipeline;Authentication & Authorization (Identity JWT OAuth)