How to do LDAP authentication on Post Request

Question

For my application, I use Spring boot and LDAP to authentication user. And I have Spring Security to control the API.

Basically what I do is to attach the Authentication: basic on the header and call the get user api(/user, get mapping) to get the user details. From there I return the pricinpal and use the user session to access the application.

@GetMapping("/user")
public Principal user(Principal user) {
      return user;
}

My question is how to do authencation on post? Same header with authentication, but the only difference is /user endpoint will be post mapping. From postman I got 401 error. Somehow LDAP isn't picking up the authentication header to do authentication.

@PostMapping("/user")
public Principal user(Principal user) {
      return user;
}

Please Help. And Thanks in advance.