Putting standard CSP login in front of a web application with a REST dispatch class

@Dmitry Maslennikov it's not actually a REST service, I just want a web application where I have full control over behavior of URLs under the application root in ObjectScript. %CSP.REST is the easiest (maybe only?) way to do that.

I ended up implementing Login as follows (which at least mostly works):

/// Called for a REST page in the event of a login being required
ClassMethod Login(skipheader As %Boolean = 1) As %Status [ ProcedureBlock = 0 ]
{
    // Support including logo image (most of the time...)
    Set brokerApp = "/csp/broker/"
    Set brokerName = $Replace(%request.URL,$Piece(%request.URL,"/portal",1),brokerApp)
    If (brokerName '= brokerApp) {
        Set filename = $System.CSP.GetFileName(brokerName)
        If ##class(%Library.File).Exists(filename) {
            Set %response.ServerSideRedirect = brokerName
            Quit $$$OK
        }
    }

    // Redirect with trailing slash (supports above)
    If ($Extract(%request.CgiEnvs("REQUEST_URI"),*) '= "/") && (%request.URL = %request.Application) {
        Set %response.Redirect = %request.Application
        Do %response.WriteHTTPHeader()
        Quit $$$OK
    }

    // Suppress "Access Denied" error message
    If %request.Method = "GET" {
        Set %request.Data("Error:ErrorCode",1) = $$$ERROR($$$RequireAuthentication)
    }

    Quit ##class(%CSP.Login).Page()
}