Spring security OAuth2 accept JSON

I am starting with Spring OAuth2. I would like to send the username and password to /oauth/token endpoint in POST body in application/json format.

curl -X POST -H "Authorization: Basic YWNtZTphY21lc2VjcmV0" -H "Content-Type: application/json" -d '{
"username": "user",
"password": "password",
"grant_type": "password"
}' "http://localhost:9999/api/oauth/token"

Is that possible?

Could you please give me an advice?

Solution (not sure if correct, but it seam that it is working):

Resource Server Configuration:

@Configuration
public class ServerEndpointsConfiguration extends ResourceServerConfigurerAdapter {

    @Autowired
    JsonToUrlEncodedAuthenticationFilter jsonFilter;

    @Override
    public void configure(HttpSecurity http) throws Exception {
        http
            .addFilterBefore(jsonFilter, ChannelProcessingFilter.class)
            .csrf().and().httpBasic().disable()
            .authorizeRequests()
            .antMatchers("/test").permitAll()
            .antMatchers("/secured").authenticated();
    }
}

Filter:

@Component
@Order(value = Integer.MIN_VALUE)
public class JsonToUrlEncodedAuthenticationFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
            ServletException {
        if (Objects.equals(request.getContentType(), "application/json") && Objects.equals(((RequestFacade) request).getServletPath(), "/oauth/token")) {
            InputStream is = request.getInputStream();
            ByteArrayOutputStream buffer = new ByteArrayOutputStream();

            int nRead;
            byte[] data = new byte[16384];

            while ((nRead = is.read(data, 0, data.length)) != -1) {
                buffer.write(data, 0, nRead);
            }
            buffer.flush();
            byte[] json = buffer.toByteArray();

            HashMap<String, String> result = new ObjectMapper().readValue(json, HashMap.class);
            HashMap<String, String[]> r = new HashMap<>();
            for (String key : result.keySet()) {
                String[] val = new String[1];
                val[0] = result.get(key);
                r.put(key, val);
            }

            String[] val = new String[1];
            val[0] = ((RequestFacade) request).getMethod();
            r.put("_method", val);

            HttpServletRequest s = new MyServletRequestWrapper(((HttpServletRequest) request), r);
            chain.doFilter(s, response);
        } else {
            chain.doFilter(request, response);
        }
    }

    @Override
    public void destroy() {
    }
}

Request Wrapper:

public class MyServletRequestWrapper extends HttpServletRequestWrapper {
    private final HashMap<String, String[]> params;

    public MyServletRequestWrapper(HttpServletRequest request, HashMap<String, String[]> params) {
        super(request);
        this.params = params;
    }

    @Override
    public String getParameter(String name) {
        if (this.params.containsKey(name)) {
            return this.params.get(name)[0];
        }
        return "";
    }

    @Override
    public Map<String, String[]> getParameterMap() {
        return this.params;
    }

    @Override
    public Enumeration<String> getParameterNames() {
        return new Enumerator<>(params.keySet());
    }

    @Override
    public String[] getParameterValues(String name) {
        return params.get(name);
    }
}

Authorization Server Configuration (disable Basic Auth for /oauth/token endpoint:

    @Configuration
public class AuthorizationServerConfiguration extends AuthorizationServerConfigurerAdapter {

    ...

    @Override
    public void configure(AuthorizationServerSecurityConfigurer oauthServer) throws Exception {
        oauthServer.allowFormAuthenticationForClients(); // Disable /oauth/token Http Basic Auth
    }

    ...

}