Protect my RESTful services by a Keycloak Oauth2 Provider Using NGINX - rest

Question

We have some Restful services on a certain URI and we wanted to publish our services on the web to use them in our mobile app(written in java),
Our services was on a server which cannot handle too much requests at a same time and used it's proxy_pass functionality for this,
So I used Nginx on an intermediate server to control access to our REST server,
Now we want to protect our services by Oauth2 with Password or Client Credentials(as our mobile users should not login into our servers we cannot display any login page to them),
I setup a Keycloak server which is working and I could get token for my client. I'm going to give my auth/token URI to our mobile developers to get Oauth2 token at first and use it in their requests.
The problem is I don't know how to configure Nginx to authorize incoming REST requests with provided token in request header.
Should I config Keycloak to Handle requests and forward authorized ones to NGINX?
Thanks for your help

Answer 1

After some tries I found this solution:
1- you have to add njs module to nginx this is necessary, you have to compile it first(so in windows it will be much trouble, I tried mingw and stopped at a dependency called expect which is not written for mingw and it wasted a lot of time from me, actually I moved our IAM to ubuntu and compiling njs and nginx in there was done in few minutes!)
2- Introspection is the key subject here, and keycloak supports it, its URI is the same as token URI plus introspect, using Basic Authorization in header and token in body
3- nginx also supports introspection after adding njs module to it, which will let nginx support js code inculde inside config file, a great exaple is NGINX Demoes- Oauth2 Introspection OSS, just copy config file and oauth2.js file and its done. I added api directive at location tag in nginx config file to let callers know it is protected.
4- create one client for nginx in keycloak to do the introspection operation, it should be in confidential mode and Service Accounts should be enabled for it.
5- nginx should forward(proxy pass) auth/token request to IAM, so a location for this should be added in config file.
6- [for ubuntu] I have an error in nginx which tells me it cannot resolve localhost! and installing Bind 9 fixes this for me(another time wasting effort was done here).
7- So any one wants to use our service should request token first and then sends its request attached with token to nginx, nginx introspects token and if token was ok and {"active": true} were received forwards request to resource and passws reply to requester.
All done.