plode( '.', $user_tokens[ $user_id ] );
			if ( empty( $user_token_chunks[1] ) || empty( $user_token_chunks[2] ) ) {
				// translators: %s is the user ID.
				return $suppress_errors ? false : new WP_Error( 'token_malformed', sprintf( __( 'Token for user %d is malformed', 'jetpack' ), $user_id ) );
			}
			if ( $user_token_chunks[2] !== (string) $user_id ) {
				// translators: %1$d is the ID of the requested user. %2$d is the user ID found in the token.
				return $suppress_errors ? false : new WP_Error( 'user_id_mismatch', sprintf( __( 'Requesting user_id %1$d does not match token user_id %2$d', 'jetpack' ), $user_id, $user_token_chunks[2] ) );
			}
			$possible_normal_tokens[] = "{$user_token_chunks[0]}.{$user_token_chunks[1]}";
		} else {
			$stored_blog_token = Jetpack_Options::get_option( 'blog_token' );
			if ( $stored_blog_token ) {
				$possible_normal_tokens[] = $stored_blog_token;
			}

			$defined_tokens_string = Constants::get_constant( 'JETPACK_BLOG_TOKEN' );

			if ( $defined_tokens_string ) {
				$defined_tokens = explode( ',', $defined_tokens_string );
				foreach ( $defined_tokens as $defined_token ) {
					if ( ';' === $defined_token[0] ) {
						$possible_special_tokens[] = $defined_token;
					} else {
						$possible_normal_tokens[] = $defined_token;
					}
				}
			}
		}

		if ( self::MAGIC_NORMAL_TOKEN_KEY === $token_key ) {
			$possible_tokens = $possible_normal_tokens;
		} else {
			$possible_tokens = array_merge( $possible_special_tokens, $possible_normal_tokens );
		}

		if ( ! $possible_tokens ) {
			// If no user tokens were found, it would have failed earlier, so this is about blog token.
			return $suppress_errors ? false : new WP_Error( 'no_possible_tokens', __( 'No blog token found', 'jetpack' ) );
		}

		$valid_token = false;

		if ( false === $token_key ) {
			// Use first token.
			$valid_token = $possible_tokens[0];
		} elseif ( self::MAGIC_NORMAL_TOKEN_KEY === $token_key ) {
			// Use first normal token.
			$valid_token = $possible_tokens[0]; // $possible_tokens only contains normal tokens because of earlier check.
		} else {
			// Use the token matching $token_key or false if none.
			// Ensure we check the full key.
			$token_check = rtrim( $token_key, '.' ) . '.';

			foreach ( $possible_tokens as $possible_token ) {
				if ( hash_equals( substr( $possible_token, 0, strlen( $token_check ) ), $token_check ) ) {
					$valid_token = $possible_token;
					break;
				}
			}
		}

		if ( ! $valid_token ) {
			if ( $user_id ) {
				// translators: %d is the user ID.
				return $suppress_errors ? false : new WP_Error( 'no_valid_user_token', sprintf( __( 'Invalid token for user %d', 'jetpack' ), $user_id ) );
			} else {
				return $suppress_errors ? false : new WP_Error( 'no_valid_blog_token', __( 'Invalid blog token', 'jetpack' ) );
			}
		}

		return (object) array(
			'secret'           => $valid_token,
			'external_user_id' => (int) $user_id,
		);
	}

	/**
	 * Updates the blog token to a new value.
	 *
	 * @access public
	 *
	 * @param string $token the new blog token value.
	 * @return Boolean Whether updating the blog token was successful.
	 */
	public function update_blog_token( $token ) {
		return Jetpack_Options::update_option( 'blog_token', $token );
	}

	/**
	 * Unlinks the current user from the linked WordPress.com user.
	 *
	 * @access public
	 * @static
	 *
	 * @todo Refactor to properly load the XMLRPC client independently.
	 *
	 * @param Integer $user_id the user identifier.
	 * @param bool    $can_overwrite_primary_user Allow for the primary user to be disconnected.
	 * @return Boolean Whether the disconnection of the user was successful.
	 */
	public function disconnect_user( $user_id, $can_overwrite_primary_user = false ) {
		$tokens = Jetpack_Options::get_option( 'user_tokens' );
		if ( ! $tokens ) {
			return false;
		}

		if ( Jetpack_Options::get_option( 'master_user' ) === $user_id && ! $can_overwrite_primary_user ) {
			return false;
		}

		if ( ! isset( $tokens[ $user_id ] ) ) {
			return false;
		}

		unset( $tokens[ $user_id ] );

		Jetpack_Options::update_option( 'user_tokens', $tokens );

		return true;
	}

	/**
	 * Returns an array of user_id's that have user tokens for communicating with wpcom.
	 * Able to select by specific capability.
	 *
	 * @param string $capability The capability of the user.
	 * @return array Array of WP_User objects if found.
	 */
	public function get_connected_users( $capability = 'any' ) {
		$connected_users = array();
		$user_tokens     = Jetpack_Options::get_option( 'user_tokens' );

		if ( ! is_array( $user_tokens ) || empty( $user_tokens ) ) {
			return $connected_users;
		}
		$connected_user_ids = array_keys( $user_tokens );

		if ( ! empty( $connected_user_ids ) ) {
			foreach ( $connected_user_ids as $id ) {
				// Check for capability.
				if ( 'any' !== $capability && ! user_can( $id, $capability ) ) {
					continue;
				}

				$user_data = get_userdata( $id );
				if ( $user_data instanceof \WP_User ) {
					$connected_users[] = $user_data;
				}
			}
		}

		return $connected_users;
	}

	/**
	 * Fetches a signed token.
	 *
	 * @param object $token the token.
	 * @return WP_Error|string a signed token
	 */
	public function get_signed_token( $token ) {
		if ( ! isset( $token->secret ) || empty( $token->secret ) ) {
			return new WP_Error( 'invalid_token' );
		}

		list( $token_key, $token_secret ) = explode( '.', $token->secret );

		$token_key = sprintf(
			'%s:%d:%d',
			$token_key,
			Constants::get_constant( 'JETPACK__API_VERSION' ),
			$token->external_user_id
		);

		$timestamp = time();

		if ( function_exists( 'wp_generate_password' ) ) {
			$nonce = wp_generate_password( 10, false );
		} else {
			$nonce = substr( sha1( wp_rand( 0, 1000000 ) ), 0, 10 );
		}

		$normalized_request_string = join(
			"\n",
			array(
				$token_key,
				$timestamp,
				$nonce,
			)
		) . "\n";

		// phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode
		$signature = base64_encode( hash_hmac( 'sha1', $normalized_request_string, $token_secret, true ) );

		$auth = array(
			'token'     => $token_key,
			'timestamp' => $timestamp,
			'nonce'     => $nonce,
			'signature' => $signature,
		);

		$header_pieces = array();
		foreach ( $auth as $key => $value ) {
			$header_pieces[] = sprintf( '%s="%s"', $key, $value );
		}

		return join( ' ', $header_pieces );
	}
}