appview/oauth: use ResumeSession when fetching currently logged in user

the final addition to my collection of oauth fixes: the session cookie
is not a sufficient indication of a logged-in-ness of a user, we
additionally validate this cookie against the session on redis using
ResumeSession and kick users out if their session is invalid.

previously, a user may have appeared to be logged in (via the profile
picture on the top right), but creating an auth'd request would have
login-prompted them.

Signed-off-by: oppiliappan <[e-mail]>

appview/oauth/oauth.go

···
 }
 
 func (o *OAuth) GetUser(r *http.Request) *User {
-	sess, err := o.SessStore.Get(r, SessionName)
-
-	if err != nil || sess.IsNew {
+	sess, err := o.ResumeSession(r)
+	if err != nil {
 		return nil
 	}
 
 	return &User{
-		Did: sess.Values[SessionDid].(string),
-		Pds: sess.Values[SessionPds].(string),
+		Did: sess.Data.AccountDID.String(),
+		Pds: sess.Data.HostURL,
 	}
 }