Add device token fetch URI generator

In order to perform the full device authorization flow it's necessary
to first generate the device code and get the authorization flow URL.

prepare_request_uri() allows us to do this while providing scopes and
additional parameters.

oauthlib/oauth2/rfc8628/clients/device.py

@@ -8,7 +8,10 @@
 """
 
 from oauthlib.oauth2 import BackendApplicationClient, Client
+from oauthlib.oauth2.rfc6749.errors import InsecureTransportError
 from oauthlib.oauth2.rfc6749.parameters import prepare_token_request
+from oauthlib.oauth2.rfc6749.utils import is_secure_transport, list_to_scope
+from oauthlib.common import add_params_to_uri
 
 
 class DeviceClient(Client):
@@ -27,6 +30,29 @@ class DeviceClient(Client):
 
     grant_type = 'urn:ietf:params:oauth:grant-type:device_code'
 
+    def __init__(self, client_id, **kwargs):
+        super().__init__(client_id, **kwargs)
+        self.client_secret = kwargs.get('client_secret')
+
+    def prepare_request_uri(self, uri, scope=None, **kwargs):
+        if not is_secure_transport(uri):
+            raise InsecureTransportError()
+
+        scope = self.scope if scope is None else scope
+        params = [(('client_id', self.client_id)), (('grant_type', self.grant_type))]
+
+        if self.client_secret is not None:
+            params.append(('client_secret', self.client_secret))
+
+        if scope:
+            params.append(('scope', list_to_scope(scope)))
+
+        for k in kwargs:
+            if kwargs[k]:
+                params.append((str(k), kwargs[k]))
+
+        return add_params_to_uri(uri, params)
+
     def prepare_request_body(self, device_code, body='', scope=None,
                              include_client_id=False, **kwargs):
         """Add device_code to request body

tests/oauth2/rfc8628/clients/test_device.py

@@ -16,13 +16,23 @@ class DeviceClientTest(TestCase):
         "require": "extra arguments"
     }
 
+    client_secret = "asecret"
+
+    device_code = "somedevicecode"
+
+    scope = ["profile", "email"]
+
     body = "not=empty"
 
     body_up = "not=empty&grant_type=urn:ietf:params:oauth:grant-type:device_code"
     body_code = body_up + "&device_code=somedevicecode"
     body_kwargs = body_code + "&some=providers&require=extra+arguments"
 
-    device_code = 'somedevicecode'
+    uri = "https://example.com/path?query=world"
+    uri_id = uri + "&client_id=" + client_id
+    uri_grant = uri_id + "&grant_type=urn:ietf:params:oauth:grant-type:device_code"
+    uri_secret = uri_grant + "&client_secret=asecret"
+    uri_scope = uri_secret + "&scope=profile+email"
 
     def test_request_body(self):
         client = DeviceClient(self.client_id)
@@ -39,3 +49,16 @@ def test_request_body(self):
         body = client.prepare_request_body(
             self.device_code, body=self.body, **self.kwargs)
         self.assertFormBodyEqual(body, self.body_kwargs)
+
+    def test_request_uri(self):
+        client = DeviceClient(self.client_id)
+
+        uri = client.prepare_request_uri(self.uri)
+        self.assertURLEqual(uri, self.uri_grant)
+
+        client = DeviceClient(self.client_id, client_secret=self.client_secret)
+        uri = client.prepare_request_uri(self.uri)
+        self.assertURLEqual(uri, self.uri_secret)
+
+        uri = client.prepare_request_uri(self.uri, scope=self.scope)
+        self.assertURLEqual(uri, self.uri_scope)