When using this particular method, if your user name or password contain any HTTP reserved characters then you will need to URL encode them. This is easily done programmatically or by using a free resource such as www.urlencoder.org. If your credentials contain white space or any of these characters you will need to encode them:

For instance, if your password was

auth&123?

that would cause a problem with the request since both & and ? have special meanings in a URL. Once encoded, this password would appear as

auth%26123%3F

which is safe to include in your request:

https://oauth2.strikeiron.com/oauth2/v2/token? client_id=user@example.com&client_secret=auth%26123%3F&grant_type=client_credentials

Note that you should only encode the specific field such as the password, not the entire URL.