Allow OPTIONS HTTP Method for oauth/token request

@EnableAuthorizationServer is adding http security configuration for endpoints like /oauth/token, /oauth/token_key etc at order 0. So what you should do is to define a http security rule for /oauth/token endpoint only for the OPTIONS http method which is at a higher order.

Something like this:

@Order(-1)
@Configuration
public class MyWebSecurity extends WebSecurityConfigurerAdapter {
   @Override
   protected void configure(HttpSecurity http) throws Exception {
       http
          .authorizeRequests()
          .antMatchers(HttpMethod.OPTIONS, "/oauth/token").permitAll()
   }
}