How do you ensure security and user verification in a microservice-based system?

In a microservices architecture, security and user verification are typically ensured through a centralized authentication and authorization system, such as OAuth 2.0 and OpenID Connect.

Main approaches:

• Using an Identity Provider (IdP): A separate service responsible for user authentication and issuing tokens (JWT).
• Access tokens: Clients receive a token after login, which they send in request headers to microservices.
• Token validation: Each microservice verifies the token's signature, expiration, and access rights (claims).
• API Gateway: Can act as a gateway that checks tokens and routes requests.
• Role-based and attribute-based authorization: At the microservice level, checks are implemented to verify user permissions for specific operations.

Example of JWT validation in an ASP.NET Core microservice:

services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
    .AddJwtBearer(options =>
    {
        options.Authority = "https://identity.example.com";
        options.Audience = "microservice_api";
    });

[Authorize]
public class ValuesController : ControllerBase
{
    // Controller methods
}

Thus, security is built on centralized authentication and distributed authorization using tokens.