Authenticate with external accounts using OIDC

After successful authentication at the provider, an account is
automatically created at docspell and the user is logged in.

modules/common/src/main/scala/docspell/common/AccountSource.scala

@@ -1,6 +1,13 @@
+/*
+ * Copyright 2020 Docspell Contributors
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
 package docspell.common
 
 import cats.data.NonEmptyList
+
 import io.circe.{Decoder, Encoder}
 
 sealed trait AccountSource { self: Product =>