Redirect URL gets prefix twice

[enolfc]

When serving galaxy in a URL with a prefix (i.e. not /), the redirect URL gets the prefix twice,
e.g. when using myprefix as galaxy_url_prefix:

http://host/myprefix/myprefix/login/start?connect_external_provider=keycloak&connect_external_email=...

I believe this is because the url_for is used both here:

galaxy/lib/galaxy/webapps/galaxy/controllers/authnz.py

Line 113 in 051c5ab

login_redirect_url=url_for("/"),

and then again below:

galaxy/lib/galaxy/webapps/galaxy/controllers/authnz.py

Line 123 in 051c5ab

return trans.response.send_redirect(url_for(redirect_url))

should this be only used the second time?