Do not pass through downstream prompt param

- throw an error when prompt=none because the spec says we can't ignore
  it
- ignore the other prompt params

Signed-off-by: Ryan Richard <richardry@vmware.com>

internal/oidc/auth/auth_handler.go

@@ -30,6 +30,8 @@ import (
 	"go.pinniped.dev/pkg/oidcclient/pkce"
 )
 
+const promptParamNone = "none"
+
 func NewHandler(
 	downstreamIssuer string,
 	idpLister oidc.UpstreamIdentityProvidersLister,
@@ -220,15 +222,6 @@ func handleAuthRequestForOIDCUpstreamAuthcodeGrant(
 		return err
 	}
 
-	if csrfFromCookie == "" {
-		// We did not receive an incoming CSRF cookie, so write a new one.
-		err := addCSRFSetCookieHeader(w, csrfValue, cookieCodec)
-		if err != nil {
-			plog.Error("error setting CSRF cookie", err)
-			return err
-		}
-	}
-
 	authCodeOptions := []oauth2.AuthCodeOption{
 		oauth2.AccessTypeOffline,
 		nonceValue.Param(),
@@ -237,8 +230,17 @@ func handleAuthRequestForOIDCUpstreamAuthcodeGrant(
 	}
 
 	promptParam := r.Form.Get("prompt")
-	if promptParam != "" && oidc.ScopeWasRequested(authorizeRequester, coreosoidc.ScopeOpenID) {
-		authCodeOptions = append(authCodeOptions, oauth2.SetAuthURLParam("prompt", promptParam))
+	if promptParam == promptParamNone && oidc.ScopeWasRequested(authorizeRequester, coreosoidc.ScopeOpenID) {
+		return writeAuthorizeError(w, oauthHelper, authorizeRequester, fosite.ErrLoginRequired)
+	}
+
+	if csrfFromCookie == "" {
+		// We did not receive an incoming CSRF cookie, so write a new one.
+		err := addCSRFSetCookieHeader(w, csrfValue, cookieCodec)
+		if err != nil {
+			plog.Error("error setting CSRF cookie", err)
+			return err
+		}
 	}
 
 	http.Redirect(w, r,

internal/oidc/auth/auth_handler_test.go

@@ -181,6 +181,12 @@ func TestAuthorizationEndpoint(t *testing.T) {
 			"error_description": "The resource owner or authorization server denied the request. Reason: required claim in upstream ID token has invalid format.",
 			"state":             happyState,
 		}
+
+		fositeLoginRequiredErrorQuery = map[string]string{
+			"error":             "login_required",
+			"error_description": "The Authorization Server requires End-User authentication.",
+			"state":             happyState,
+		}
 	)
 
 	hmacSecretFunc := func() []byte { return []byte("some secret - must have at least 32 bytes") }
@@ -630,7 +636,7 @@ func TestAuthorizationEndpoint(t *testing.T) {
 			wantDownstreamPKCEChallengeMethod: downstreamPKCEChallengeMethod,
 		},
 		{
-			name:                                   "OIDC upstream browser flow happy path with prompt param login passed through to redirect uri",
+			name:                                   "OIDC upstream browser flow happy path with prompt param other than none that gets ignored",
 			idps:                                   oidctestutil.NewUpstreamIDPListerBuilder().WithOIDC(upstreamOIDCIdentityProvider()),
 			generateCSRF:                           happyCSRFGenerator,
 			generatePKCE:                           happyPKCEGenerator,
@@ -645,9 +651,26 @@ func TestAuthorizationEndpoint(t *testing.T) {
 			wantContentType:                        htmlContentType,
 			wantBodyStringWithLocationInHref:       true,
 			wantCSRFValueInCookieHeader:            happyCSRF,
-			wantLocationHeader:                     expectedRedirectLocationForUpstreamOIDC(expectedUpstreamStateParam(map[string]string{"prompt": "login"}, "", ""), "login"),
+			wantLocationHeader:                     expectedRedirectLocationForUpstreamOIDC(expectedUpstreamStateParam(map[string]string{"prompt": "login"}, "", ""), ""),
 			wantUpstreamStateParamInLocationHeader: true,
 		},
+		{
+			name:               "OIDC upstream browser flow with prompt param none throws an error because we want to independently decide the upstream prompt param",
+			idps:               oidctestutil.NewUpstreamIDPListerBuilder().WithOIDC(upstreamOIDCIdentityProvider()),
+			generateCSRF:       happyCSRFGenerator,
+			generatePKCE:       happyPKCEGenerator,
+			generateNonce:      happyNonceGenerator,
+			stateEncoder:       happyStateEncoder,
+			cookieEncoder:      happyCookieEncoder,
+			method:             http.MethodGet,
+			path:               modifiedHappyGetRequestPath(map[string]string{"prompt": "none"}),
+			contentType:        "application/x-www-form-urlencoded",
+			body:               encodeQuery(happyGetRequestQueryMap),
+			wantStatus:         http.StatusFound,
+			wantContentType:    "application/json; charset=utf-8",
+			wantLocationHeader: urlWithQuery(downstreamRedirectURI, fositeLoginRequiredErrorQuery),
+			wantBodyString:     "",
+		},
 		{
 			name:            "OIDC upstream browser flow with error while decoding CSRF cookie just generates a new cookie and succeeds as usual",
 			idps:            oidctestutil.NewUpstreamIDPListerBuilder().WithOIDC(upstreamOIDCIdentityProvider()),