feat: add basic structure of idp templates (#5053)

add basic structure and implement first providers for IDP templates to be able to manage and use them in the future

internal/idp/providers/gitlab/gitlab.go

@@ -0,0 +1,35 @@
+package gitlab
+
+import (
+	"github.com/zitadel/zitadel/internal/idp"
+	"github.com/zitadel/zitadel/internal/idp/providers/oidc"
+)
+
+const (
+	issuer = "https://gitlab.com"
+	name   = "GitLab"
+)
+
+var _ idp.Provider = (*Provider)(nil)
+
+// Provider is the [idp.Provider] implementation for Gitlab
+type Provider struct {
+	*oidc.Provider
+}
+
+// New creates a GitLab.com provider using the [oidc.Provider] (OIDC generic provider)
+func New(clientID, clientSecret, redirectURI string, options ...oidc.ProviderOpts) (*Provider, error) {
+	return NewCustomIssuer(name, issuer, clientID, clientSecret, redirectURI, options...)
+}
+
+// NewCustomIssuer creates a GitLab provider using the [oidc.Provider] (OIDC generic provider)
+// with a custom issuer for self-managed instances
+func NewCustomIssuer(name, issuer, clientID, clientSecret, redirectURI string, options ...oidc.ProviderOpts) (*Provider, error) {
+	rp, err := oidc.New(name, issuer, clientID, clientSecret, redirectURI, oidc.DefaultMapper, options...)
+	if err != nil {
+		return nil, err
+	}
+	return &Provider{
+		Provider: rp,
+	}, nil
+}