Generate cryptographically secure random strings. Based on Kohana's Text::random() method and this answer:http://stackoverflow.com/a/13733588/179104

cryptographically_secure_random_strings.php

function random_text( $type = 'alnum', $length = 8 )
{
	switch ( $type ) {
		case 'alnum':
			$pool = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
			break;
		case 'alpha':
			$pool = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
			break;
		case 'hexdec':
			$pool = '0123456789abcdef';
			break;
		case 'numeric':
			$pool = '0123456789';
			break;
		case 'nozero':
			$pool = '123456789';
			break;
		case 'distinct':
			$pool = '2345679ACDEFHJKLMNPRSTUVWXYZ';
			break;
		default:
			$pool = (string) $type;
			break;
	}


	$crypto_rand_secure = function ( $min, $max ) {
		$range = $max - $min;
		if ( $range < 0 ) return $min; // not so random...
		$log    = log( $range, 2 );
		$bytes  = (int) ( $log / 8 ) + 1; // length in bytes
		$bits   = (int) $log + 1; // length in bits
		$filter = (int) ( 1 << $bits ) - 1; // set all lower bits to 1
		do {
			$rnd = hexdec( bin2hex( openssl_random_pseudo_bytes( $bytes ) ) );
			$rnd = $rnd & $filter; // discard irrelevant bits
		} while ( $rnd >= $range );
		return $min + $rnd;
	};

	$token = "";
	$max   = strlen( $pool );
	for ( $i = 0; $i < $length; $i++ ) {
		$token .= $pool[$crypto_rand_secure( 0, $max )];
	}
	return $token;
}