feat: add saml request to link to sessions (#9001)

# Which Problems Are Solved

It is currently not possible to use SAML with the Session API.

# How the Problems Are Solved

Add SAML service, to get and resolve SAML requests.
Add SAML session and SAML request aggregate, which can be linked to the
Session to get back a SAMLResponse from the API directly.

# Additional Changes

Update of dependency zitadel/saml to provide all functionality for
handling of SAML requests and responses.

# Additional Context

Closes #6053

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

cmd/start/start.go

@@ -49,6 +49,7 @@ import (
 	user_v3_alpha "github.com/zitadel/zitadel/internal/api/grpc/resources/user/v3alpha"
 	userschema_v3_alpha "github.com/zitadel/zitadel/internal/api/grpc/resources/userschema/v3alpha"
 	"github.com/zitadel/zitadel/internal/api/grpc/resources/webkey/v3"
+	saml_v2 "github.com/zitadel/zitadel/internal/api/grpc/saml/v2"
 	session_v2 "github.com/zitadel/zitadel/internal/api/grpc/session/v2"
 	session_v2beta "github.com/zitadel/zitadel/internal/api/grpc/session/v2beta"
 	settings_v2 "github.com/zitadel/zitadel/internal/api/grpc/settings/v2"
@@ -530,7 +531,7 @@ func startAPIs(
 		store,
 		consolePath,
 		oidcServer.AuthCallbackURL(),
-		provider.AuthCallbackURL(samlProvider),
+		samlProvider.AuthCallbackURL(),
 		config.ExternalSecure,
 		userAgentInterceptor,
 		op.NewIssuerInterceptor(oidcServer.IssuerFromRequest).Handler,
@@ -555,6 +556,10 @@ func startAPIs(
 	if err := apis.RegisterService(ctx, oidc_v2.CreateServer(commands, queries, oidcServer, config.ExternalSecure)); err != nil {
 		return nil, err
 	}
+	// After SAML provider so that the callback endpoint can be used
+	if err := apis.RegisterService(ctx, saml_v2.CreateServer(commands, queries, samlProvider, config.ExternalSecure)); err != nil {
+		return nil, err
+	}
 	// handle grpc at last to be able to handle the root, because grpc and gateway require a lot of different prefixes
 	apis.RouteGRPC()
 	return apis, nil