Is there an easy way to generate Captcha String in swift? [closed]

I have to implement captcha for verification in the login page of my application. The captcha must be a combo of lower, upper case letters and numbers.

eg: W3q5L0.

I am generating random letters & nums for each character of the string now. i.e for each letter in the captcha, I am generating a lowercase letter, a number for the next character and upper case letter for the 3rd character etc.

I am pretty sure that this is a long way of doing this. so I wanted to get opinion from you all for an easier method.