WIP: Add login handler for LDAP/AD web login

Also change state param to include IDP type

internal/oidc/login/login_handler.go

@@ -0,0 +1,23 @@
+// Copyright 2022 the Pinniped contributors. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package login
+
+import (
+	"net/http"
+)
+
+// NewHandler returns an http.Handler that serves the login endpoint for IDPs that
+//  don't have their own Web UI.
+func NewHandler() http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodGet {
+			http.Error(w, `Method not allowed (try GET)`, http.StatusMethodNotAllowed)
+			return
+		}
+		_, err := w.Write([]byte("<p>hello world</p>"))
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusInternalServerError)
+		}
+	})
+}

internal/oidc/oidc.go

@@ -1,4 +1,4 @@
-// Copyright 2020-2021 the Pinniped contributors. All Rights Reserved.
+// Copyright 2020-2022 the Pinniped contributors. All Rights Reserved.
 // SPDX-License-Identifier: Apache-2.0
 
 // Package oidc contains common OIDC functionality needed by Pinniped.
@@ -26,13 +26,14 @@ const (
 	CallbackEndpointPath      = "/callback"
 	JWKSEndpointPath          = "/jwks.json"
 	PinnipedIDPsPathV1Alpha1  = "/v1alpha1/pinniped_identity_providers"
+	PinnipedLoginPath         = "/login"
 )
 
 const (
 	// Just in case we need to make a breaking change to the format of the upstream state param,
 	// we are including a format version number. This gives the opportunity for a future version of Pinniped
 	// to have the consumer of this format decide to reject versions that it doesn't understand.
-	UpstreamStateParamFormatVersion = "1"
+	UpstreamStateParamFormatVersion = "2"
 
 	// The `name` passed to the encoder for encoding the upstream state param value. This name is short
 	// because it will be encoded into the upstream state param value and we're trying to keep that small.
@@ -93,6 +94,7 @@ type Codec interface {
 type UpstreamStateParamData struct {
 	AuthParams    string              `json:"p"`
 	UpstreamName  string              `json:"u"`
+	UpstreamType  string              `json:"t"`
 	Nonce         nonce.Nonce         `json:"n"`
 	CSRFToken     csrftoken.CSRFToken `json:"c"`
 	PKCECode      pkce.Code           `json:"k"`