Verify Keycloak token from two different URLs

I have a Docker compose based system with back-end and front-end components. The back-end is written in Python Flask and run in several docker containers and front-end is written in TypeScript with Angular. The front-end communicates with back-end via Restful APIs. The proxy is created with Nginx. But the Keycloak Token verification doesn't work between front-end and back-end.

My KeyCloak (and MySQL) section of docker-compose.yml file:

  mysql:
    image: mysql:5.7.31
    ports:
      - 9988:3306
    volumes:
      - keycloak_data:/var/lib/mysql
    environment:
      MYSQL_ROOT_PASSWORD: root
      MYSQL_DATABASE: keycloak
      MYSQL_USER: keycloak
      MYSQL_PASSWORD: password
    networks:
      - auth_net

  keycloak:
    image: jboss/keycloak:13.0.1
    environment:
      DB_VENDOR: MYSQL
      DB_ADDR: mysql
      DB_DATABASE: keycloak
      DB_USER: keycloak
      DB_PASSWORD: password
      KEYCLOAK_USER: admin
      KEYCLOAK_PASSWORD: admin
      PROXY_ADDRESS_FORWARDING: "true"
    ports:
      - 8080:8080
      - 8443:8443
    depends_on:
      - mysql
    networks:
      - auth_net

Related Nginx config part:

    location /api/auth/verify {
        internal;
        proxy_method POST;
        proxy_intercept_errors on;
        proxy_pass http://keycloak:8080/auth/realms/master/protocol/openid-connect/userinfo;
        error_page 400 =401 /401.html;
    }

I use the above /api/auth/verify URL for every endpoints as verification. Eg.:

    location /api/users {
        auth_request /api/auth/verify;
        rewrite ^/api/(.*) /$1  break;
        proxy_pass http://users:6000;
        proxy_pass_request_headers on;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }

My Keycloak config for TypeScript/Angular:

export const environment = {
  production: false,
  keycloakConfig: {
    url: 'http://localhost:8080/auth/',
    realm: 'master',
    clientId: 'frontend'
  }
};

app-init.ts:

import { KeycloakService, KeycloakOptions } from 'keycloak-angular';
import { environment } from 'src/environments/environment';

export function initializer(keycloak: KeycloakService): () => Promise<any> {
  const options: KeycloakOptions = {
    config: environment.keycloakConfig
  };

  return (): Promise<any> => keycloak.init(options);
}

My app.module.ts file contains the following section:

  providers: [
    KeycloakService,
    {
      provide: APP_INITIALIZER,
      useFactory: initializer,
      multi: true,
      deps: [KeycloakService]
    }
  ]

The getting error:

Config of frontend client in Keycloak:

My problem in points:

• The Nginx uses the http://keycloak:8080 URL which is the network inside the docker system (The Nginx doesn't see the localhost from Docker).
• The front-end (TS/Angular) uses the http://localhost:8080 URL which is visible from outside (from the users' browser) (In theory the front-end doesn't see the keycloak network from user's browser)
• When I send a request from front-end which calls my API (which want to verify the token based on above Nginx example), I get Invalid Token error
• Based on my investigation I get this error because I get the token on http://localhost:8080 URL and I want to verify it on http://keycloak:8080 URL.

Summarize of my used URLs:

• API's URL: http://localhost
• Keycloak URL inside Docker: http://keycloak:8080
• Keycloak on front-end side: http://localhost:8080
• Fornt-end's URL : http://localhost:4200

My question:

• How can I solve the above problem? I am very open for ideas.

1. EDIT:

If I have tried to set the front-end URL to http://localhost:8080, and http://localhost:4200 but I got the below issue in both cases: