Support for prompt=create in keycloak.js

[mposolda]

Description

There was this functionality added in Keycloak 26.1 keycloak/keycloak#10701 . It is standard way how can client notify Keycloak that it wants to open user registrations screen rather than login screen .

The keycloak.js supports the functionality by the proprietary registrations endpoint https://github.com/keycloak/keycloak/blob/26.0.7/js/libs/keycloak-js/lib/keycloak.js#L839 . But the endpoint is now deprecated. It can be nice to update this to use prompt=create instead of registrations endpoint, so we can eventually remove the endpoint in Keycloak 27 ( keycloak/keycloak#36084 ) without keycloak.js being broken.

At the same time, it can be nice if we keep the support for registrations endpoint for the cases when keycloak.js is used with older Keycloak server versions than 26.1. Not sure if there is a mechanism in keycloak.js to detect server version or if it needs to be some configuration option in keycloak.js to specify which way to use (prompt=create VS registrations endpoint)?

Discussion

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Motivation

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Details

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[jonkoops]

We can probably use the .well-known/openid-configuration endpoint to make sure this remains backwards compatible.

[mposolda]

@jonkoops +1 . It has option prompt_values_supported, which is now returned in the well-known endpoint response. But this property prompt_values_supported was recently added (also in Keycloak 26.1 in the same commit like the prompt=create) .

So if the prompt_values_supported exists and contains create, we know that prompt=create is supported. Otherwise we know that we need to stick with the legacy endpooint.