Spring boot Authenticate Rest API using Google OAuth2 and how to test using Postman

I have created the Spring boot Rest API and authenticating using Google OAuth2.

I am testing GET API using browser it is working fine. However, I need to test POST api, i am using POSTMAN and getting unwired HTML response.

pom.xml -------- included dependency.

<dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-oauth2-client</artifactId>
</dependency> 

Created Config-------------

public class OAuthConfig extends WebSecurityConfigurerAdapter {    
    @Override
    public void configure(HttpSecurity http) throws Exception {
    http.csrf().disable().antMatcher("/**")
    .authorizeRequests()
    .antMatchers("/")
    .permitAll()
    .anyRequest()
    .authenticated().and().oauth2Login().and().oauth2Client();
    }
    }

=========================

    @GetMapping(value = "/hello", produces = "application/json")
    public Principal getHello(Principal principal) {
    return principal;
    }

This rest point is working fine with browser after authenticating using gmail user and password. Principal render the JOSN object on Browser. after hitting url http:localhost:8081/hello "idToken":{ "tokenValue": However, It is not working with POSTMAN.

Please someone help me to test POST API using POSTMAN.