Hi,
You're right, the consumer key can be anything you like. You need to enter it in the tool settings in the consumer site. The first time the tool is launched, the provider will store information about the consumer, including the key you've used.
I will point out that there are implications to using different consumer keys across different tools on the consumer site, however. Because the Moodle provider code uses the consumer key in generating unique identifiers for user accounts, using different consumer keys can result in two user accounts being created on the provider, for the same user on the consumer site. This would occur if the same user launched two tools on the consumer using different consumer keys (i.e each tool is set up to use a different consumer key). If your use case is a single organisation using the tool(s), you probably want to just pick a key and stick with it, making sure that all launches a given user will result in that same account being reused on the provider site.
Hope that helps
Jake
