If I wanted to kick the tires with developing for the desire2learn platform, but don't have a desire2learn installation to develop against, can I use the valence.desire2learn.com environment. How can I get a user login for that environment? Do I get one when I request an app developer key?
There are two steps you can take as a Valence API user to get yourself working:
Download a client library and work with it, and the getting started sample, to get up and running against 'valence.desire2learn.com'. The sample has a set of test App credentials, and a test user that you can use to make one or two simple calls: get the product version table from the test LMS, and get the 'whoami' information for the test user.
You can use this level of bootstrapping to get your self up to the stage where you have a client framework that can go through the authentication process with an LMS, and then create authenticated URls to make API calls against an LMS.
The next step for real work requires you to have an LMS against which you can work, and a user account on that LMS. There are several scenarios you can try here:
Work with an existing vendor or institution that does have a test environment you can test against.
Go through the steps required to become a D2L Partner: once you do that, the partnership program can provide you with a test LMS you can use for your development needs.