Best way to hash two values into one? I'm trying to hash two unique strings together to create a hash. The most obvious way would be simply to concatenate the two and run a hash function on it:

hash = sha256(strA + strB)


But I was wondering if this is how most people do it, and if there is a "standard" way of doing something like this in a most secure way.
The most important thing you're missing is that you should combine the two strings with an injective function: a function such that every unique combination of inputs determines a unique output.  

Your idea to just concatenate the two strings violates this condition.  One example is that "abc" + "def" is the same string as "ab" + "cdef" or "abcd" + "ef".  Whether an adversary can exploit this to their advantage depends on the application, but there's no reason to expose oneself to this risk to start with.

Some techniques for combining strings in an injective fashion:


Put an unambiguous delimiter between the strings
Prepend each string with its length


Another tip: whichever method you pick, write a function that can "split" any combined string back into its components, and a bunch of test cases to show that the property split(combine(strA, strB)) == (strA, strB) holds for all values of strA and strB.