You can aready read random bytes: https://golang.org/pkg/math/rand/#Read

If that is not enough, you should clarify why. As far as I can see, as long as you can obtain any amount of random bytes, you can do anything from there.

Thanks for your response. Yes, there is rand.Read but you don't have control over the output characters. Sometimes you need to generate a random string based on a given character set.
I think of something like this:
rand.String("AZXEgewdd1234$#!@*&")

That's a higher level abstraction you could build on top of random bytes or integers. There's really no reason to put it in the package API. Different people will want different kinds of "random strings" too, so I also doubt that a single API would be universally useful.