Configure mounts dispatch app

src/dispatch/fastapi.py

@@ -2,9 +2,42 @@
 
 """
 
+import os
 import fastapi
+from fastapi.responses import PlainTextResponse
 
 
-def configure(app: fastapi.FastAPI):
-    """Configure the FastAPI app to use Dispatch programmable endpoints."""
-    ...
+def configure(
+    app: fastapi.FastAPI,
+    api_key: None | str = None,
+    api_url: str = "https://api.stealthrocket.cloud",
+    mount_path: str = "/dispatch",
+):
+    """Configure the FastAPI app to use Dispatch programmable endpoints.
+
+    Args:
+        app: The FastAPI app to configure.
+        api_key: Dispatch API key to use for authentication. Uses the value of
+          the DISPATCH_API_KEY environment variable by default.
+        api_url: URL of the Dispatch service.
+        mount_path: The path to mount Dispatch programmable endpoints at.
+    """
+    api_key = api_key or os.environ.get("DISPATCH_API_KEY")
+    api_url = api_url or "https://api.stealthrocket.cloud"
+
+    if not app:
+        raise ValueError("app is required")
+    if not api_key:
+        raise ValueError("api_key is required")
+    if not api_url:
+        raise ValueError("api_url is required")
+    if not mount_path:
+        raise ValueError("mount_path is required")
+
+    dispatch_app = fastapi.FastAPI()
+
+    @dispatch_app.get("/", response_class=PlainTextResponse)
+    def read_root():
+        return "ok"
+
+    app.mount(mount_path, dispatch_app)

tests/test_fastapi.py

@@ -9,12 +9,19 @@ class TestFastAPI(unittest.TestCase):
     def test_fastapi(self):
         app = fastapi.FastAPI()
 
-        dispatch.fastapi.configure(app)
+        dispatch.fastapi.configure(app, api_key="test-key")
 
         @app.get("/")
         def read_root():
             return {"Hello": "World"}
 
         client = TestClient(app)
+
+        # Ensure existing routes are still working.
         resp = client.get("/")
         self.assertEqual(resp.status_code, 200)
+
+        # Ensure Dispatch root is working.
+        resp = client.get("/dispatch/")
+        self.assertEqual(resp.status_code, 200)
+        self.assertEqual(resp.text, "ok")