keycloak provides different issuer for frontend and backend

Question

I am new to keycloak, I am using keycloak for both frontend and backend application but I am getting the different issuer in the token generated by keycloak when decoded in jwt.io.

Front end:

• the issuer is the same as the base URL of the frontend application
• For example:

  If the front-end URL is https://example.org/portal then the issuer is the same as https://example.org/auth

Request via postman:

• the issuer is the internal DNS name

I have tried below ways,

1. Proxy redirection(With preserve host) - Which generates the issuer with frontend base url.
2. Proxy redirection without preserving host - Which expects the private DNS to be resolved at front end application
3. Played around the keycloak configuration - updated frontendUrl to https://example.org/auth and forceBackendUrlToFrontendUrl to true which resulted in the same issuer both the backend and frontend but no hostname like https:/auth/relam/external(Refer #2 in reference).

Expected outcome:

• I need the private DNS to be issuer it both the request from frontend and backend(for now it works direct backend request)

Thanks in advance.

Reference

1. https://github.com/keycloak/keycloak-community/blob/master/design/hostname-default-provider.md
2. Code block

<spi name="hostname">
 <default-provider>fixed</default-provider>
 <provider name="fixed" enabled="true">
  <properties>
   <property name="frontendUrl" value="https://example.org/auth"/>
   <property name="forceBackendUrlToFrontendUrl" value="true"/>
  </properties>
 </provider>
</spi>