✨(backend) add file specific admin

Adds a file (background image) specific django admin.
Files can be previewed, and deletion is properly managed.

src/backend/core/utils.py

@@ -459,6 +459,41 @@ def generate_upload_policy(file):
     return policy
 
 
+def generate_download_file_url(file, *, expires_in: int, override_domain: bool = True):
+    """
+    Generate a S3 signed download url for a given file.
+    """
+
+    key = file.file_key
+
+    # This setting should be used if the backend application and the frontend application
+    # can't connect to the object storage with the same domain. This is the case in the
+    # docker compose stack used in development. The frontend application will use localhost
+    # to connect to the object storage while the backend application will use the object storage
+    # service name declared in the docker compose stack.
+    # This is needed because the domain name is used to compute the signature. So it can't be
+    # changed dynamically by the frontend application.
+    if settings.AWS_S3_DOMAIN_REPLACE and override_domain:
+        s3_client = boto3.client(
+            "s3",
+            aws_access_key_id=settings.AWS_S3_ACCESS_KEY_ID,
+            aws_secret_access_key=settings.AWS_S3_SECRET_ACCESS_KEY,
+            endpoint_url=settings.AWS_S3_DOMAIN_REPLACE,
+            config=botocore.client.Config(
+                region_name=settings.AWS_S3_REGION_NAME,
+                signature_version=settings.AWS_S3_SIGNATURE_VERSION,
+            ),
+        )
+    else:
+        s3_client = default_storage.connection.meta.client
+
+    return s3_client.generate_presigned_url(
+        ClientMethod="get_object",
+        Params={"Bucket": default_storage.bucket_name, "Key": key},
+        ExpiresIn=expires_in,
+    )
+
+
 @lru_cache(maxsize=1)
 def _format_telephony_phone_number(raw_number, default_country):
     """Parse a configured phone number and return (country, international_format).