nginx - njs - ngx_http_auth_request_module how to return 302 to user?

I am using njs ngx_http_auth_request_module.

I have js function like this;

function introspectAccessToken(r) {
    r.subrequest("/_oauth2_send_request",
        function(reply) {
            if (reply.status == 200) {
                r.return(204); // Token is valid, return success code
            } else {
                // need 302 here
            }
        }
    );
}

The documentation says "If the subrequest returns a 2xx response code, the access is allowed. If it returns 401 or 403, the access is denied with the corresponding error code. Any other response code returned by the subrequest is considered an error." http://nginx.org/en/docs/http/ngx_http_auth_request_module.html

I need to return 302 to user if subsequest enters "else" block.

Is there anyway to achieve this? If I set r.return(302), it shows Error page in browser as documentation said.

edit: my nginx.conf

location /my-webclient {
    auth_request /_oauth2_token_introspection;
    root   /usr/share/nginx/html;
    rewrite ^ /hmb-profile-webclient/index.html break;
}       

location = /_oauth2_token_introspection {
    internal;
    js_content introspectAccessToken;                                       
}   

location /_oauth2_send_request {
    internal;
    proxy_method      POST;
    proxy_set_body    $cookie_jwt;
    proxy_pass http://my-specific-url;
}   

http://my-specific-url returns

• 200, if jwt cookie is valid
• 302 (with return location), if jwt cookie is invalid

Got it - I don't think you even need njs to do this. In case your token introspection endpoint is NOT build with NJS and its not validating the if the token is a valid json but it is implemented with some other language this NGINX config will work.

#cache for auth_request responses

proxy_cache_path /var/cache/nginx/oauth keys_zone=token_responses:1m max_size=2m;

#Your Server
server {

  listen 80;


  location / {
    #Redirect Unauthed Request to some other location... 
    error_page 401 =302 http://localhost:9000/login;
  
    auth_request /_auth_request;
    proxy_pass http://127.0.0.1:8080;


  }

  location /_auth_request {
    internal;
    proxy_pass http://127.0.0.1:8090;
    ###place caching responses here to be more effective;
    proxy_cache           token_responses; # Enable caching
    proxy_cache_key       $cookie_jwt;    # Cache for each access token
    proxy_cache_lock      on;              # Duplicate tokens must wait
    proxy_cache_valid     200 10s;         # How long to use each response
    proxy_ignore_headers  Cache-Control Expires Set-Cookie;
  }


}

....

In case you want to build more logic with NJS like validate the token structure your approach was the right one using NJS with js_set.

js_include oauth2.js; # Location of JavaScript code

server {
    listen 80;

    location / {
        error_page 401 403 =302 http://localhost:9000/login;
        auth_request /_oauth2_token_introspection;
        proxy_pass http://my_backend;
    }

    location = /_oauth2_token_introspection {
        internal;
        js_content introspectAccessToken;                                       
    }

njs function

function introspectAccessToken(r) {
    r.subrequest("/_oauth2_send_request",
        function(reply) {
            if (reply.status == 200) {
                var response = JSON.parse(reply.responseBody);
                if (response.active == true) {
                    r.return(204); // Token is valid, return success code
                } else {
                    r.return(403); // Token is invalid, return forbidden code
                }
            } else {
                r.return(401); // Unexpected response, return 'auth required'
            }
        }
    );
}

The error_page directive will work likewise. Based on you code I assume you already checked out this article?

https://www.nginx.com/blog/validating-oauth-2-0-access-tokens-nginx/

ICYMI it's a great blog post about this use case.