Hey SmartThings Developers!
We recently made an update to improve the security around how we accept OAuth access token requests. The common use case for this is if you are writing a Web Services SmartApp, and need to get an access token to make requests to it.
This change aligns us closer to the OAuth 2 specification (RFC 6749) and is a good improvement!
It might, however, mean that the way in which you request access tokens might need to be updated. See the docs for more info.