The SitePoint PHP blog has a post from author Nicola Pietroluongo talking about randomness in PHP. In the tutorial he talks about randomness, how it relates to cryptography and what's coming in PHP 7 to help.

This article analyzes problems related to random number generation used for cryptography purposes. PHP 5 does not provide an easy mechanism for generating cryptographically strong random numbers, while PHP 7 solves this by introducing a couple of CSPRNG functions.

He starts off by talking about what a CSPRNG (cryptographically secure pseudorandom number generator) is and some of the things it could be used for. He then moves on to the functionality coming in PHP 7 with the addition of the random_* functions for getting random bytes and random integer values. He talks briefly about what's going on "behind the scenes" of the generation and provides a simple code example with a randomized "dice roll" and the resulting numbers. He ends the post mentioning the random_compat library that can be installed for pre-PHP 7 applications that provides the same functionality just without those two functions defined.

The Paragon Initiative blog has posted a guide to what they see as a way to safely generate random strings and integers in PHP applications.

Generating useful random data is a fairly common task for a developer to implement, but also one that developers rarely get right. [...] It's generally not okay to use a weak random number generator unless both of the following two conditions are met: the security of your application does not depend in any way on the value you generate being unpredictable or there is no requirement for each value to be unique (up to a reasonable probability).

He gives some examples of places where it's a must to use a "cryptographically secure pseudo-random number generator" including generating random passwords, encryption keys or IVs for data in CBC mode. The article goes on to talk about some of the problems that could come from using weak generators. It then gets into the process for generating random values and the use of the random_* functions in PHP (or using this polyfill) to more safely generate the numbers. Included is code showing the process and some advice around converting random bytes to both strings and integers.