Fix malformed ActivityPub handles for email-based logins

.github/changelog/2082-from-description

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fixed
+
+Fix malformed ActivityPub handles for users with email-based logins (e.g., from Site Kit Google authentication)

includes/model/class-user.php

@@ -169,7 +169,14 @@ public function get_alternate_url() {
 	 * @return string The preferred username.
 	 */
 	public function get_preferred_username() {
-		return \get_the_author_meta( 'login', $this->_id );
+		$login = \get_the_author_meta( 'login', $this->_id );
+
+		// Handle cases where login is an email address (e.g., from Site Kit Google login).
+		if ( \filter_var( $login, FILTER_VALIDATE_EMAIL ) ) {
+			$login = \str_replace( array( '@', '.' ), '-', $login );
+		}
+
+		return $login;
 	}
 
 	/**

tests/includes/model/class-test-user.php

@@ -128,4 +128,50 @@ public function test_get_moved_to() {
 		$this->assertArrayHasKey( 'movedTo', $user );
 		$this->assertSame( 'https://example.com', $user['movedTo'] );
 	}
+
+	/**
+	 * Test that email-based usernames are properly sanitized for ActivityPub handles.
+	 *
+	 * @covers ::get_preferred_username
+	 * @covers ::get_webfinger
+	 */
+	public function test_email_username_sanitization() {
+		// Test with email-based login (e.g., from Site Kit Google login).
+		$user_id = self::factory()->user->create(
+			array(
+				'role'       => 'author',
+				'user_login' => '[email protected]',
+			)
+		);
+		$user    = User::from_wp_user( $user_id );
+
+		// Preferred username should be sanitized.
+		$this->assertSame( 'testuser123-gmail-com', $user->get_preferred_username() );
+
+		// Webfinger should not have double @.
+		$expected_webfinger = 'testuser123-gmail-com@' . \wp_parse_url( \home_url(), \PHP_URL_HOST );
+		$this->assertSame( $expected_webfinger, $user->get_webfinger() );
+
+		// Test another email format.
+		$user_id2 = self::factory()->user->create(
+			array(
+				'role'       => 'author',
+				'user_login' => '[email protected]',
+			)
+		);
+		$user2    = User::from_wp_user( $user_id2 );
+
+		$this->assertSame( 'admin-googlemail-com', $user2->get_preferred_username() );
+
+		// Test normal username (no email) remains unchanged.
+		$user_id3 = self::factory()->user->create(
+			array(
+				'role'       => 'author',
+				'user_login' => 'normaluser',
+			)
+		);
+		$user3    = User::from_wp_user( $user_id3 );
+
+		$this->assertSame( 'normaluser', $user3->get_preferred_username() );
+	}
 }