If you are provided with a password, this may be the secret you need to use.
I'd try adding the tool manually. Go to Site administration > Plugins > Activity modules > External tool > Manage tools and click "configure a tool manually". The link should be pasted into "Tool URL". Then set shared secret to the "password" you were given. If you weren't given a "key" or "username" try just typing anything there, for instance your site name. You may want to just make it all one word. E.g. "acmecorporation"
Let me know if this helps.