Description:
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Including Base64-encoded data in URLs and file names is a commonly encountered task.  The PHP base64_encode() function is not suitable for this, since its output may encode the characters "+" (which has special meaning in URL query parameters) and "/" (which is used as a path separator in file names and URL paths).

RFC 4648 (http://tools.ietf.org/html/rfc4648) defines, in section 5, a standard variant of Base64 encoding, called "base64url", for this purpose.  It differs from the usual "base64" format in that the characters "+" and "/" are replaced with "-" and "_" respectively, and that the use of the padding character "=" is optional and not usually recommended.

I would like to suggest that functions for encoding and decoding data in this format be provided in PHP alongside the existing base64_encode() and base64_decode() functions.  Although such functions can be relatively easily implemented in pure PHP code based on the existing Base64 encoding functions, a built-in implementation would presumably be both more efficient and more likely to be user correctly by script authors.

A sample PHP implementation of the proposed functions (which could be included in the documentation for backward compatibility purposes) is included below:

    function base64url_encode( $data, $pad = false ) {
        $base64 = strtr( base64_encode( $data ), '+/', '-_' );
        return ( $pad ? $base64 : rtrim( $base64, '=' ) );
    }

    function base64url_decode( $base64, $strict = false ) {
        return base64_decode( strtr( $base64, '-_+/', '+/-_' ), $strict );
    }