[Bambora] Where is «MD5 Key» in the merchant interface?

It is in the «Security/Authentication» block:

bambora--hash-key

As you can see, «MD5 Key» is a bad name, because the hash algorithm could be not only «MD5», but «SHA-1» too, and «SHA-1» is the default value.
So, actually «MD5 Key» is a hash key.

See also: