1. Software background: The server runs the service, and the client program cannot access the service. The service can be called normally using WCFTestClient.

2. Exception message: SOAP security negotiation with ‘HTTP… ‘ for target ‘http… ‘ failed.
3. Solutions:
A. Find the following information in the client configuration file:

        <identity>
          <userPrincipalName value="XXX" />
        </identity>

B. Delete this section.
4. Q&a: this configuration item USES NTLM for authentication. No changes are made when debugging locally. When the server is deployed, you need to consider.