Keycloak: Invalid token issuer when running from internal docker container
Might be related to this answer on here: https://stackoverflow.com/a/64095482/13494285
You could set Host header value to be the expected url.
To override this behavior, you might try to set KEYCLOAK_HOSTNAME environment variable to be the expected url.
Seems like documentation might not be up-to-date (it suggests KEYCLOAK_FRONTEND_URL variable on here), but instead KEYCLOAK_HOSTNAME is used to set fixed provider, as seen on here.
On this context, also the KEYCLOAK_HTTP_PORT is required to set the port to be 8080