Log generic Exceptions to ERROR with stack trace

Log Exceptions to ERROR. Protocol Exceptions are treated in separate ExceptionHandlers, but generic Exceptions like NPEs must be logged with full stack trace

Fixes gh-1545

Author: jbiblio

spring-security-oauth2/src/main/java/org/springframework/security/oauth2/provider/endpoint/TokenEndpoint.java

@@ -165,8 +165,8 @@ public ResponseEntity<OAuth2Exception> handleHttpRequestMethodNotSupportedExcept
 
 	@ExceptionHandler(Exception.class)
 	public ResponseEntity<OAuth2Exception> handleException(Exception e) throws Exception {
-		if (logger.isWarnEnabled()) {
-			logger.warn("Handling error: " + e.getClass().getSimpleName() + ", " + e.getMessage());
+		if (logger.isErrorEnabled()) {
+			logger.error("Handling error: " + e.getClass().getSimpleName() + ", " + e.getMessage(), e);
 		}
 		return getExceptionTranslator().translate(e);
 	}