http://localhost:8080/oauth/token?grant_type=client_credentials&scope=select&client_id=client_1&client_secret=123456

{
    "access_token": "b0f73d20-1c74-43f6-991d-3b4ca74fc4d4",
    "token_type": "bearer",
    "expires_in": 41374,
    "scope": "select"
}

{
"expiration": 1513752144897,
"expired": false,
"expiresIn": 604799,
"refreshToken": {
"expiration": 1515739344897,
"value": "dae50004-939c-40f2-98d8-4882374e08c7"
},
"scope": [
"api"
],
"tokenType": "bearer",
"value": "1e2c4181-01be-4aa1-8042-c2d2f74008d0"
}

public class OAuth2AccessTokenMessageConverter extends AbstractHttpMessageConverter<OAuth2AccessToken> {

    private final FastJsonHttpMessageConverter delegateMessageConverter;

    public OAuth2AccessTokenMessageConverter() {
        super(MediaType.APPLICATION_JSON);
        this.delegateMessageConverter = new FastJsonHttpMessageConverter();
    }

    @Override
    protected boolean supports(Class<?> clazz) {
        return OAuth2AccessToken.class.isAssignableFrom(clazz);
    }

    @Override
    protected OAuth2AccessToken readInternal(Class<? extends OAuth2AccessToken> clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException {
        throw new UnsupportedOperationException(
                "This converter is only used for converting from externally aqcuired form data");
    }

    @Override
    protected void writeInternal(OAuth2AccessToken accessToken, HttpOutputMessage outputMessage) throws IOException,
            HttpMessageNotWritableException {
        Map<String, Object> data = new HashMap<>(8);
        data.put(OAuth2AccessToken.ACCESS_TOKEN, accessToken.getValue());
        data.put(OAuth2AccessToken.TOKEN_TYPE, accessToken.getTokenType());
        data.put(OAuth2AccessToken.EXPIRES_IN, accessToken.getExpiresIn());
        data.put(OAuth2AccessToken.SCOPE, String.join(" ", accessToken.getScope()));
        OAuth2RefreshToken refreshToken = accessToken.getRefreshToken();
        if (Objects.nonNull(refreshToken)) {
            data.put(OAuth2AccessToken.REFRESH_TOKEN, refreshToken.getValue());
        }
        delegateMessageConverter.write(data, MediaType.APPLICATION_JSON, outputMessage);
    }

}

@Configuration
public class Oauth2WebMvcConfigurer implements WebMvcConfigurer {

    @Override
    public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
       converters.add(0, new FastJsonHttpMessageConverter());
       converters.add(0, new OAuth2AccessTokenMessageConverter());
    }
}