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/google/google.go

@@ -0,0 +1,47 @@
+package google
+
+import (
+	openid "github.com/zitadel/oidc/v2/pkg/oidc"
+
+	"github.com/zitadel/zitadel/internal/idp"
+	"github.com/zitadel/zitadel/internal/idp/providers/oidc"
+)
+
+const (
+	issuer = "https://accounts.google.com"
+	name   = "Google"
+)
+
+var _ idp.Provider = (*Provider)(nil)
+
+// Provider is the [idp.Provider] implementation for Google
+type Provider struct {
+	*oidc.Provider
+}
+
+// New creates a Google provider using the [oidc.Provider] (OIDC generic provider)
+func New(clientID, clientSecret, redirectURI string, opts ...oidc.ProviderOpts) (*Provider, error) {
+	rp, err := oidc.New(name, issuer, clientID, clientSecret, redirectURI, userMapper, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return &Provider{
+		Provider: rp,
+	}, nil
+}
+
+var userMapper = func(info openid.UserInfo) idp.User {
+	return &User{oidc.DefaultMapper(info)}
+}
+
+// User is a representation of the authenticated Google and implements the [idp.User] interface
+// by wrapping an [idp.User] (implemented by [oidc.User]). It overwrites the [GetPreferredUsername] to use the `email` claim.
+type User struct {
+	idp.User
+}
+
+// GetPreferredUsername implements the [idp.User] interface.
+// It returns the email, because Google does not return a username.
+func (u *User) GetPreferredUsername() string {
+	return u.GetEmail()
+}