Also, never name the classmethod in disp or impl Login() or login() - it compiles, but the IRIS CSP/REST-API  engine doesn't work with such names - it seems they are reserved ones.

Also, make sure you DON'T change the method nomenclature in the impl class - spec compilation will change it (not touching the methods' implementation, though). It can cost you some time to investigate what's going on, as this will appear in the deployment phase only.

e.g. consider method in the impl class:

Classmethod foo (bar as %String) as %Status {
 if bar="" write "bar is empty."
return $$$OK
}

If you change nomenclature, e.g. introduce the default value

Classmethod foo (bar as %String ="" ) as %Status {
 if bar="" write "bar is empty."
return $$$OK
}

It will work on a dev stage, and you will have class with a default value in your GitHub repository, but once the solution is deployed, the spec file compilation will change the nomenclature back to the original "without default" stage, as it is stated according to specs:

Classmethod foo (bar as %String ) as %Status {
 if bar="" write "bar is empty."
return $$$OK
}