✨(backend) add server-to-server API endpoint to create documents

We want trusted external applications to be able to create documents
via the API on behalf of any user. The user may or may not pre-exist
in our database and should be notified of the document creation by
email.

src/backend/core/services/converter_services.py

@@ -0,0 +1,76 @@
+"""Converter services."""
+
+from django.conf import settings
+
+import requests
+
+
+class ConversionError(Exception):
+    """Base exception for conversion-related errors."""
+
+
+class ValidationError(ConversionError):
+    """Raised when the input validation fails."""
+
+
+class ServiceUnavailableError(ConversionError):
+    """Raised when the conversion service is unavailable."""
+
+
+class InvalidResponseError(ConversionError):
+    """Raised when the conversion service returns an invalid response."""
+
+
+class MissingContentError(ConversionError):
+    """Raised when the response is missing required content."""
+
+
+class YdocConverter:
+    """Service class for conversion-related operations."""
+
+    @property
+    def auth_header(self):
+        """Build microservice authentication header."""
+        return f"Bearer {settings.CONVERSION_API_KEY}"
+
+    def convert_markdown(self, text):
+        """Convert a Markdown text into our internal format using an external microservice."""
+
+        if not text:
+            raise ValidationError("Input text cannot be empty")
+
+        try:
+            response = requests.post(
+                settings.CONVERSION_API_URL,
+                json={
+                    "content": text,
+                },
+                headers={
+                    "Authorization": self.auth_header,
+                    "Content-Type": "application/json",
+                },
+                timeout=settings.CONVERSION_API_TIMEOUT,
+            )
+            response.raise_for_status()
+            conversion_response = response.json()
+
+        except requests.RequestException as err:
+            raise ServiceUnavailableError(
+                "Failed to connect to conversion service",
+            ) from err
+
+        except ValueError as err:
+            raise InvalidResponseError(
+                "Could not parse conversion service response"
+            ) from err
+
+        try:
+            document_content = conversion_response[
+                settings.CONVERSION_API_CONTENT_FIELD
+            ]
+        except KeyError as err:
+            raise MissingContentError(
+                f"Response missing required field: {settings.CONVERSION_API_CONTENT_FIELD}"
+            ) from err
+
+        return document_content