🗃️(models) remove 'secret' field from mailbox model

We remove 'secret' field, as it won't be of use in interactions
between la Régie and dimail. Régie credentials will be stored and used
as project variable.

src/backend/mailbox_manager/utils/dimail.py

@@ -30,14 +30,16 @@ class DimailAPIClient:
 
     API_URL = settings.MAIL_PROVISIONING_API_URL
 
-    def get_headers(self, domain):
+    def get_headers(self):
         """Build header dict from domain object."""
         # self.secret is the encoded basic auth, to request a new token from dimail-api
         headers = {"Content-Type": "application/json"}
 
         response = requests.get(
             f"{self.API_URL}/token/",
-            headers={"Authorization": f"Basic {domain.secret}"},
+            headers={
+                "Authorization": f"Basic {settings.MAIL_PROVISIONING_API_CREDENTIALS}"
+            },
             timeout=20,
         )
 
@@ -48,8 +50,8 @@ class DimailAPIClient:
 
         if response.status_code == status.HTTP_403_FORBIDDEN:
             logger.error(
-                "[DIMAIL] 403 Forbidden: please check the mail domain secret of %s",
-                domain.name,
+                "[DIMAIL] 403 Forbidden: Could not retrieve a token,\
+                please check 'MAIL_PROVISIONING_API_CREDENTIALS' setting.",
             )
             raise exceptions.PermissionDenied
 
@@ -68,7 +70,7 @@ class DimailAPIClient:
             response = session.post(
                 f"{self.API_URL}/domains/{mailbox.domain}/mailboxes/{mailbox.local_part}/",
                 json=payload,
-                headers=self.get_headers(mailbox.domain),
+                headers=self.get_headers(),
                 verify=True,
                 timeout=10,
             )
@@ -98,7 +100,7 @@ class DimailAPIClient:
 
         if response.status_code == status.HTTP_403_FORBIDDEN:
             raise exceptions.PermissionDenied(
-                f"Secret not valid for this domain {mailbox.domain.name}"
+                "Permission denied. Please check your MAIL_PROVISIONING_API_CREDENTIALS."
             )
 
         return self.pass_dimail_unexpected_response(response)