fix: recover from rejected Canvas refresh tokens and add token admin

src/canvas_oauth/admin.py

@@ -0,0 +1,15 @@
+from django.contrib import admin
+
+from canvas_oauth.models import CanvasOAuth2Token
+
+
+@admin.register(CanvasOAuth2Token)
+class CanvasOAuth2TokenAdmin(admin.ModelAdmin):
+    list_display = ["user", "created_on", "updated_on", "expires"]
+    search_fields = ["user__username", "user__email"]
+    # Tokens only come from the OAuth flow; the admin is for viewing and deleting
+    exclude = ["access_token", "refresh_token"]
+    readonly_fields = ["user", "expires", "created_on", "updated_on"]
+
+    def has_add_permission(self, request):
+        return False

src/canvas_oauth/canvas.py

@@ -4,7 +4,7 @@
 import requests
 from django.utils import timezone
 
-from canvas_oauth.exceptions import InvalidOAuthReturnError
+from canvas_oauth.exceptions import InvalidOAuthReturnError, InvalidGrantError
 from canvas_oauth import settings
 
 logger = logging.getLogger(__name__)
@@ -85,6 +85,8 @@ def get_access_token(
     r = requests.post(oauth_token_url, post_params)
     logger.info("%s POST response from Canvas is %s", grant_type, r.text)
     if r.status_code != 200:
+        if r.status_code in (400, 401) and _error_code(r) == "invalid_grant":
+            raise InvalidGrantError("%s grant was rejected: %s" % (grant_type, r.text))
         raise InvalidOAuthReturnError(
             "%s request failed to get a token: %s" % (grant_type, r.text)
         )
@@ -104,3 +106,10 @@ def get_access_token(
         refresh_token = response_data["refresh_token"]
 
     return (access_token, expires, refresh_token)
+
+
+def _error_code(response):
+    try:
+        return response.json().get("error")
+    except ValueError:
+        return None

src/canvas_oauth/exceptions.py

@@ -12,3 +12,9 @@ class InvalidOAuthStateError(CanvasOAuthError):
 
 class InvalidOAuthReturnError(CanvasOAuthError):
     pass
+
+
+class InvalidGrantError(InvalidOAuthReturnError):
+    """Canvas no longer recognizes the grant (e.g. the refresh token was revoked)"""
+
+    pass

src/canvas_oauth/oauth.py

@@ -11,7 +11,11 @@
 
 from canvas_oauth import canvas, settings
 from canvas_oauth.models import CanvasOAuth2Token
-from canvas_oauth.exceptions import MissingTokenError, InvalidOAuthStateError
+from canvas_oauth.exceptions import (
+    MissingTokenError,
+    InvalidOAuthStateError,
+    InvalidGrantError,
+)
 
 logger = logging.getLogger(__name__)
 
@@ -96,11 +100,13 @@ def oauth_callback(request):
         code=code,
     )
 
-    CanvasOAuth2Token.objects.create(
+    CanvasOAuth2Token.objects.update_or_create(
         user=request.user,
-        access_token=access_token,
-        expires=expires,
-        refresh_token=refresh_token,
+        defaults={
+            "access_token": access_token,
+            "expires": expires,
+            "refresh_token": refresh_token,
+        },
     )
 
     return redirect(request.session["canvas_oauth_initial_uri"])
@@ -134,13 +140,20 @@ def refresh_oauth_token(request):
 
     # Get the new access token and expiration date via
     # a refresh token grant
-    oauth_token.access_token, oauth_token.expires, _ = canvas.get_access_token(
-        grant_type="refresh_token",
-        client_id=settings.CANVAS_OAUTH_CLIENT_ID,
-        client_secret=settings.CANVAS_OAUTH_CLIENT_SECRET,
-        redirect_uri=request.build_absolute_uri(reverse("canvas-oauth-callback")),
-        refresh_token=oauth_token.refresh_token,
-    )
+    try:
+        oauth_token.access_token, oauth_token.expires, _ = canvas.get_access_token(
+            grant_type="refresh_token",
+            client_id=settings.CANVAS_OAUTH_CLIENT_ID,
+            client_secret=settings.CANVAS_OAUTH_CLIENT_SECRET,
+            redirect_uri=request.build_absolute_uri(reverse("canvas-oauth-callback")),
+            refresh_token=oauth_token.refresh_token,
+        )
+    except InvalidGrantError:
+        # Canvas no longer recognizes the refresh token (revoked, key reset, etc.),
+        # so drop it and send the user back through authorization
+        logger.warning("Refresh token rejected for user %s", request.user.pk)
+        oauth_token.delete()
+        raise MissingTokenError("Refresh token rejected for user %s" % request.user.pk)
 
     # Update the model with new token and expiration
     oauth_token.save()