Bad Request for SSO Request URI?

Request URI:

https://<CUCM SERVER>:8443/ssosp/oauth/authorize?scope=UnifiedCommunications:readwrite&response_type=token&client_id=<TOKEN>&redirect_uri=http%3A%2F%2F<APP ADDRESS>%2Fsample%2Fredirect.html

Error Response:

{"error":INVALID_REQUEST,"error_description":"The request is missing a required parameter, includes an invalid parameter value, includes a parameter more than once, or is otherwise malformed."}

If you are using the Jabber Web SDK, then SSO transactions (including building the SSO kickoff URI) are mostly transparently handled for you:

If you are using either CUCM/UDS or CUC/CUMI APIs instead, then this tutorial is relevant:

https://developer.cisco.com/site/sso/

Specific to building the request URI:

Cisco DevNet: SSO

Make sure the redirect URI has been configured on CUCM.  Confirm it is set under System/Enterprise Parameters/SSO Configuration/Redirect URIs for Third Party SSO Client:

(if there are two are more, then each should be comma-separated)

The URL here would need to be your app's redirect page.