Spring/OAuth2 Error - InsufficientAuthenticationException, There is no client authentication. Try adding an appropriate authentication filter

I've been stuck for hours trying to figure out what in the world is going wrong with this Spring Security OAuth2 implementation.

The error occurs when I go to hit the /oauth/token endpoint:

localhost:8080/my-oauth-practice-app/oauth/token

Error: InsufficientAuthenticationException, There is no client authentication. Try adding an appropriate authentication filter.

AUTHORIZATION SERVER CONFIGURATION

@Configuration
@EnableAuthorizationServer
public class AuthorizationServerConfig extends AuthorizationServerConfigurerAdapter {


    @Autowired
    @Qualifier("authenticationManagerBean")
    AuthenticationManager authenticationManager;

    @Autowired
    DefaultTokenServices tokenServices;

    @Override
    public void configure(AuthorizationServerEndpointsConfigurer endpoints) throws Exception {
        super.configure(endpoints);
        endpoints.tokenServices(this.tokenServices).authenticationManager(this.authenticationManager);

    }

    @Override
    public void configure(AuthorizationServerSecurityConfigurer security) throws Exception {
        super.configure(security);
        security.tokenKeyAccess("permitAll()");
    }

    @Override
    public void configure(ClientDetailsServiceConfigurer clients) throws Exception {
        clients.inMemory().withClient("clientid").secret("clientpass").authorizedGrantTypes("password").scopes("read").autoApprove(true);
    }


}

RESOURCE SERVER CONFIGURATION

@Configuration
@EnableResourceServer
public class ResourceServerConfig extends ResourceServerConfigurerAdapter {

    @Autowired
    DefaultTokenServices tokenServices;

    @Override
    public void configure(ResourceServerSecurityConfigurer resources) throws Exception {
        super.configure(resources);
        resources.tokenServices(this.tokenServices);
    }

    @Override
    public void configure(HttpSecurity http) throws Exception {
        super.configure(http);
        http.authorizeRequests().anyRequest().hasRole("USER");
    }

}

GENERAL WEB SECURITY CONFIGURATION

@Configuration
@EnableWebSecurity
@EnableGlobalMethodSecurity(prePostEnabled = true)
public class WebSecurityConfig extends WebSecurityConfigurerAdapter {

    @Primary
    @Bean
    DefaultTokenServices tokenServices() {
        DefaultTokenServices d = new DefaultTokenServices();
        d.setAccessTokenValiditySeconds(600);
        d.setRefreshTokenValiditySeconds(1000);
        d.setTokenStore(new InMemoryTokenStore());
        return d;
    }

    @Override
    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
        auth.inMemoryAuthentication().withUser("user").password("password").roles("USER");
    }

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests().antMatchers("/**").hasRole("USER");
    }


    @Override
    @Bean
    public AuthenticationManager authenticationManagerBean() throws Exception {
        return super.authenticationManagerBean();
    }

}