feat(op): allow scope without openid (#613)

This changes removes the requirement of the openid scope to be set for all token requests.
As this library also support OAuth2-only authentication mechanisms we still want to sanitize requested scopes, but not enforce the openid scope.

Related to https://github.com/zitadel/zitadel/discussions/8068

pkg/op/auth_request.go

@@ -11,6 +11,7 @@ import (
 	"net"
 	"net/http"
 	"net/url"
+	"slices"
 	"strings"
 	"time"
 
@@ -250,37 +251,23 @@ func ValidateAuthReqPrompt(prompts []string, maxAge *uint) (_ *uint, err error)
 	return maxAge, nil
 }
 
-// ValidateAuthReqScopes validates the passed scopes
+// ValidateAuthReqScopes validates the passed scopes and deletes any unsupported scopes.
+// An error is returned if scopes is empty.
 func ValidateAuthReqScopes(client Client, scopes []string) ([]string, error) {
 	if len(scopes) == 0 {
 		return nil, oidc.ErrInvalidRequest().
 			WithDescription("The scope of your request is missing. Please ensure some scopes are requested. " +
 				"If you have any questions, you may contact the administrator of the application.")
 	}
-	openID := false
-	for i := len(scopes) - 1; i >= 0; i-- {
-		scope := scopes[i]
-		if scope == oidc.ScopeOpenID {
-			openID = true
-			continue
-		}
-		if !(scope == oidc.ScopeProfile ||
+	scopes = slices.DeleteFunc(scopes, func(scope string) bool {
+		return !(scope == oidc.ScopeOpenID ||
+			scope == oidc.ScopeProfile ||
 			scope == oidc.ScopeEmail ||
 			scope == oidc.ScopePhone ||
 			scope == oidc.ScopeAddress ||
 			scope == oidc.ScopeOfflineAccess) &&
-			!client.IsScopeAllowed(scope) {
-			scopes[i] = scopes[len(scopes)-1]
-			scopes[len(scopes)-1] = ""
-			scopes = scopes[:len(scopes)-1]
-		}
-	}
-	if !openID {
-		return nil, oidc.ErrInvalidScope().WithDescription("The scope openid is missing in your request. " +
-			"Please ensure the scope openid is added to the request. " +
-			"If you have any questions, you may contact the administrator of the application.")
-	}
-
+			!client.IsScopeAllowed(scope)
+	})
 	return scopes, nil
 }
 

pkg/op/auth_request_test.go

@@ -137,11 +137,6 @@ func TestValidateAuthRequest(t *testing.T) {
 			args{&oidc.AuthRequest{}, mock.NewMockStorageExpectValidClientID(t), nil},
 			oidc.ErrInvalidRequest(),
 		},
-		{
-			"scope openid missing fails",
-			args{&oidc.AuthRequest{Scopes: []string{"profile"}}, mock.NewMockStorageExpectValidClientID(t), nil},
-			oidc.ErrInvalidScope(),
-		},
 		{
 			"response_type missing fails",
 			args{&oidc.AuthRequest{Scopes: []string{"openid"}}, mock.NewMockStorageExpectValidClientID(t), nil},
@@ -287,16 +282,6 @@ func TestValidateAuthReqScopes(t *testing.T) {
 				err: true,
 			},
 		},
-		{
-			"scope openid missing fails",
-			args{
-				mock.NewClientExpectAny(t, op.ApplicationTypeWeb),
-				[]string{"email"},
-			},
-			res{
-				err: true,
-			},
-		},
 		{
 			"scope ok",
 			args{