Nginx return dynamic JSON response in error_page

Question

I have 2 REST applications: main API and Auth API. I configured Nginx above them, so that the request goes to auth API first and if auth succeeded, continues in main API.

When Auth API returns 401 or 403, I would like to return error code to the client in response as JSON. However, as I googled, Nginx doesn't support passing response body to the client from auth_request. So I thought I could set the error code in Auth API as a response header and generate JSON response from it in Nginx using error_page directive. Here is my Nginx configuration:

server {
    listen       80;
    server_name  127.0.0.1;

    if_modified_since off;
    expires off;
    etag off;

    set $api_base_url "http://api:9090";
    set $service_user_base_url "http://auth-api:9091";

    resolver 127.0.0.11 ipv6=off;

    location /some-api-endpoint {
        auth_request /validate_token;
        auth_request_set $authorization $upstream_http_authorization;

        proxy_pass $api_base_url;
        proxy_intercept_errors on;
        add_header Authorization $authorization;

        error_page 401 = @handle_auth_401;
        error_page 403 = @handle_auth_403;
    }

    location = /validate_token {
        internal;
        if ($request_method = OPTIONS) {
            return 200;
        }
        proxy_pass  $service_user_base_url/validation;
        proxy_pass_request_body off;
        proxy_set_header X-Original-URI $request_uri;
        proxy_set_header X-Original-Method $request_method;
    }

    location @handle_auth_401 {
        default_type application/json;
        return 401 '{"failure":{"type":"$upstream_http_x_auth_failed_error_code"}}';
    }

    location @handle_auth_403 {
        default_type application/json;
        return 403 '{"failure":{"type":"$upstream_http_x_auth_failed_error_code"}}';
    }
}

However, the response I receive is {"failure":{"type":""}}. When I call auth API's /validation endpoint, I receive the header 'X-Auth-Failed-Error-Code' in response, but for some reason Nginx can't resolve it. Seems like I miss something.

Have someone tried this or faced the same problem before? Would really appreciate any help.

UPD:

Okay, I have managed to solve this issue, using another auth_request_set directive in API location:

    location /some-api-endpoint {
        auth_request /validate_token;
        auth_request_set $authorization $upstream_http_authorization;
        auth_request_set $x_auth_failed_error_code $sent_http_x_auth_failed_error_code;
...

Then I use new variable in named location like this:

    location @handle_auth_401 {
        default_type application/json;
        return 401 '{"failure":{"type":"$x_auth_failed_error_code"}}';
    }

Nginx return dynamic JSON response in error_page

0 Answers0