WP_REST_Request::get_header_as_array( string $key )

Source

File: wp-includes/rest-api/class-wp-rest-request.php

public function get_header_as_array( $key ) {
		$key = $this->canonicalize_header_name( $key );

		if ( ! isset( $this->headers[ $key ] ) ) {
			return null;
		}

		return $this->headers[ $key ];
	}