Don't show the login form again after successful login
Move the OAuth2 authentication to a separate class
Add Basic authentication support
Switch to Basic authentication

The OAuth2 auth page at https://www.ne.se/oauth/token appears to be
broken, occasionally returning a 502 Proxy Error with the following
message:

 The proxy server received an invalid response from an upstream server.
 The proxy server could not handle the request POST /oauth/token.
 Reason: DNS lookup failure for: apoc.neint.se

Switch to the (deprecated) basic authentication of the API as a
workaround.  This unfortunately means that the credentials are now sent
in plain text.
v1.8