It seems that queryParams are not populated in [0]: (there is no assignment)

I think at the two places [1] [2] where the queryParameterMap is build 

uriInfo.getQueryParameters() should be used.

[0] https://github.com/keycloak/keycloak/blob/337f39009010705346e28dab8ea326a53acdb5bf/services/src/main/java/org/keycloak/forms/login/freemarker/FreeMarkerLoginFormsProvider.java#L94

[1] https://github.com/keycloak/keycloak/blob/337f39009010705346e28dab8ea326a53acdb5bf/services/src/main/java/org/keycloak/forms/login/freemarker/FreeMarkerLoginFormsProvider.java#L181

[2] https://github.com/keycloak/keycloak/blob/337f39009010705346e28dab8ea326a53acdb5bf/services/src/main/java/org/keycloak/forms/login/freemarker/FreeMarkerLoginFormsProvider.java#L334

Cheers,

Thomas