[FIX] webservice: WARNING message in logs

The use of a compute method on ``oauth2_flow`` when this field is touched by
the server environment mixin causes it to be defined twice as computed,
with differents settings, and this ultimately causes a warning message
in the logs:

```
WARNING odoo odoo.modules.registry: webservice.backend: inconsistent 'compute_sudo' for computed fields: protocol, url, auth_type, username, password, api_key, api_key_header, oauth2_flow, oauth2_clientid, oauth2_client_secret, oauth2_token_url, oauth2_authorization_url, oauth2_audience, oauth2_scope, content_type
```

We fix this by overriding method ``compute_server_env()``

webservice/models/webservice_backend.py

@@ -39,8 +39,6 @@ class WebserviceBackend(models.Model):
             ("web_application", "Web Application (Authorization Code Grant)"),
         ],
         readonly=False,
-        store=True,
-        compute="_compute_oauth2_flow",
     )
     oauth2_clientid = fields.Char(string="Client ID", auth_type="oauth2")
     oauth2_client_secret = fields.Char(string="Client Secret", auth_type="oauth2")
@@ -122,12 +120,6 @@ def _get_adapter_protocol(self):
             protocol += f"+{self.auth_type}-{self.oauth2_flow}"
         return protocol
 
-    @api.depends("auth_type")
-    def _compute_oauth2_flow(self):
-        for rec in self:
-            if rec.auth_type != "oauth2":
-                rec.oauth2_flow = False
-
     @api.depends("auth_type", "oauth2_flow")
     def _compute_redirect_url(self):
         get_param = self.env["ir.config_parameter"].sudo().get_param
@@ -177,3 +169,10 @@ def _server_env_fields(self):
         }
         webservice_fields.update(base_fields)
         return webservice_fields
+
+    def _compute_server_env(self):
+        # OVERRIDE: reset ``oauth2_flow`` when ``auth_type`` is not "oauth2", even if
+        # defined otherwise in server env vars
+        res = super(WebserviceBackend, self)._compute_server_env()
+        self.filtered(lambda r: r.auth_type != "oauth2").oauth2_flow = None
+        return res

webservice/tests/test_oauth2.py

@@ -9,6 +9,9 @@
 import responses
 from oauthlib.oauth2.rfc6749.errors import InvalidGrantError
 
+from odoo.addons.server_environment import server_env
+from odoo.addons.server_environment.models import server_env_mixin
+
 from .common import CommonWebService, mock_cursor
 
 
@@ -213,3 +216,33 @@ def test_fetch_token_from_auth(self):
         adapter = self.webservice._get_adapter()
         token = adapter._fetch_token_from_authorization(code)
         self.assertEqual("cool_token", token["access_token"])
+
+    def test_oauth2_flow_compute(self):
+        # Test with current configuration
+        env = os.environ
+        self.assertIn("auth_type = oauth2\n", env["SERVER_ENV_CONFIG"])
+        self.assertIn("oauth2_flow = web_application\n", env["SERVER_ENV_CONFIG"])
+        server_env_mixin.serv_config = server_env._load_config()  # Reload env vars
+        self.webservice.invalidate_recordset()  # Force recomputation when reading
+        self.assertEqual(self.webservice.oauth2_flow, "web_application")
+
+        # Update configuration: ``auth_type`` is changed to ``none``
+        env["SERVER_ENV_CONFIG"] = env["SERVER_ENV_CONFIG"].replace(
+            "auth_type = oauth2", "auth_type = none"
+        )
+        server_env_mixin.serv_config = server_env._load_config()  # Reload env vars
+        self.webservice.invalidate_recordset()  # Clear cache => read forces compute
+        self.assertFalse(self.webservice.oauth2_flow)
+
+        # Update configuration: ``auth_type`` is reverted to ``oauth2``,
+        # and ``oauth2_flow`` is updated to ``backend_application``
+        env["SERVER_ENV_CONFIG"] = (
+            env["SERVER_ENV_CONFIG"]
+            .replace("auth_type = none", "auth_type = oauth2")
+            .replace(
+                "oauth2_flow = web_application", "oauth2_flow = backend_application"
+            )
+        )
+        server_env_mixin.serv_config = server_env._load_config()  # Reload env vars
+        self.webservice.invalidate_recordset()  # Clear cache => read forces compute
+        self.assertEqual(self.webservice.oauth2_flow, "backend_application")