Call another Microservice in Event Handler #9540

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  AI-Bot created 14 days ago

  Support Team ABP Agent

  • In ABP microservice architecture, when Microservice B (event handler) needs to call a protected API on Microservice C, you must ensure that B can authenticate itself to C. Since the event is not triggered by a user HTTP request, you cannot forward a user access token. The recommended approach is to use client credentials flow for service-to-service communication.

  • Steps:

    1. Register Microservice B as a client in your IdentityServer (AuthServer) with the necessary scopes/permissions to call Microservice C.
    2. In Microservice B, implement a service to acquire and cache a client credentials access token from IdentityServer.
    3. When handling the event, use this token to authenticate HTTP requests to Microservice C.
    4. Configure Microservice C to accept and validate tokens from registered clients.

  • Example (token acquisition in B):

    var client = new HttpClient();
    var disco = await client.GetDiscoveryDocumentAsync("https://identity-server-url");
    var tokenResponse = await client.RequestClientCredentialsTokenAsync(new ClientCredentialsTokenRequest
    {
        Address = disco.TokenEndpoint,
        ClientId = "microservice-b-client-id",
        ClientSecret = "microservice-b-secret",
        Scope = "microservice-c-scope"
    });
    var accessToken = tokenResponse.AccessToken;
    

  • Use this accessToken in the Authorization header when calling C:

    client.SetBearerToken(accessToken);
    var response = await client.GetAsync("https://microservice-c/api/protected-endpoint");
    

  • ABP provides infrastructure to automate this with dynamic HTTP clients and remoting modules. See the "Zero Trust Microservice Architecture" article for a full implementation, including token caching and automatic renewal.

  Sources:

  • Zero Trust Microservice Architecture with ABP Framework
  • ABP Microservice Tutorial: Distributed Events

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