mitreid-connect/OpenID-Connect-Java-Spring-Server — pull request #708 by jmandel (2014-10-17 16:02:57+00:00)
Title: Omit uninformative error_description

This is an API usability thing: when a client displays an error to the user, how does the client know what text to show on the screen?

rfc6749 says:

```
error_description
OPTIONAL. Human-readable ASCII [USASCII] text providing
additional information, used to assist the client developer in
understanding the error that occurred.
```

If there's no "additional information" to convey, the `error_description` shouldn't be populated. Leaving the message null will cause `error_description` to be omitted [in Spring secoauth](https://github.com/spring-projects/spring-security-oauth/blob/master/spring-security-oauth2/src/main/java/org/springframework/security/oauth2/common/exceptions/OAuth2Exception.java#L176).

(This was an issue for us when trying to automatically decide what message to display on the screen in case of errors.)