Pre-fill username field in login-form via GET parameter (using OIDC protocol)

[Christian Migowski]

Hi,

is it possible to pre-fill the username field on the login form using the OIDC protocol?

I had a look at the template and there is a parameter openIdLocalId which enables this.

I created and configured the following LoginDecorator-Groovy script and it works as expected when calling the login endpoint directly: 

def run(Object[] args) {

    def requestContext = args[0]

    def applicationContext = args[1]

    def logger = args[2]

    // Url parameter can not be 'username' because cas uses this parameter

    String usrName = requestContext.getRequestParameters().get("usrName")

    if(usrName != null) {

        logger.info("using preset username from request parameters: " + usrName)

        requestContext.getFlowScope().put("openIdLocalId", usrName)

    }

}

Unfortunately when using OIDC the clients never call the /login endpoint directly but instead first call the /authorize endpoint, which then internally redirects to the /login endpoint - where unfortunately the additional request parameter gets lost, rendering the script effect-less.

I scanned through the code, read the documentation and searched the web but I couldnt find any information about it, the name "openIdLocalId" may imply that it's got something to do with OIDC but I really cannot figure out how to do it.

If there is another way to achieve this I would be happy to learn about it!

The usecase is that a client application requests the user to enter its username and then decides depending on this to which IdP ( i.e. there are multiple) the user will be redirected, the user shouldnt be required to enter his username again after the re-direct to the IdP.

Thanks and best regards,

christian