feature(cli): login flow fixes and improvements (#16052)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: yurijmikhalevich

src/lightning_app/cli/lightning_cli.py

@@ -205,7 +205,7 @@ def login() -> None:
     auth.clear()
 
     try:
-        auth._run_server()
+        auth.authenticate()
     except ConnectionError:
         click.echo(f"Unable to connect to {get_lightning_cloud_url()}. Please check your internet connection.")
         exit(1)

src/lightning_app/utilities/login.py

@@ -4,6 +4,7 @@
 import pathlib
 from dataclasses import dataclass
 from enum import Enum
+from time import sleep
 from typing import Optional
 from urllib.parse import urlencode
 
@@ -44,9 +45,11 @@ def __post_init__(self):
             setattr(self, key.suffix, os.environ.get(key.value, None))
 
         self._with_env_var = bool(self.user_id and self.api_key)  # used by authenticate method
-        if self.api_key and not self.user_id:
+        if self._with_env_var:
+            self.save("", self.user_id, self.api_key, self.user_id)
+            logger.info("Credentials loaded from environment variables")
+        elif self.api_key or self.user_id:
             raise ValueError(
-                f"{Keys.USER_ID.value} is missing from env variables. "
                 "To use env vars for authentication both "
                 f"{Keys.USER_ID.value} and {Keys.API_KEY.value} should be set."
             )
@@ -135,7 +138,8 @@ def authenticate(self) -> Optional[str]:
 
 
 class AuthServer:
-    def get_auth_url(self, port: int) -> str:
+    @staticmethod
+    def get_auth_url(port: int) -> str:
         redirect_uri = f"http://localhost:{port}/login-complete"
         params = urlencode(dict(redirectTo=redirect_uri))
         return f"{get_lightning_cloud_url()}/sign-in?{params}"
@@ -144,6 +148,7 @@ def login_with_browser(self, auth: Auth) -> None:
         app = FastAPI()
         port = find_free_network_port()
         url = self.get_auth_url(port)
+
         try:
             # check if server is reachable or catch any network errors
             requests.head(url)
@@ -156,32 +161,42 @@ def login_with_browser(self, auth: Auth) -> None:
                 f"An error occurred with the request. Please report this issue to Lightning Team \n{e}"  # E501
             )
 
-        logger.info(f"login started for lightning.ai, opening {url}")
+        logger.info(
+            "\nAttempting to automatically open the login page in your default browser.\n"
+            'If the browser does not open, navigate to the "Keys" tab on your Lightning AI profile page:\n\n'
+            f"{get_lightning_cloud_url()}/me/keys\n\n"
+            'Copy the "Headless CLI Login" command, and execute it in your terminal.\n'
+        )
         click.launch(url)
 
         @app.get("/login-complete")
         async def save_token(request: Request, token="", key="", user_id: str = Query("", alias="userID")):
-            if token:
-                auth.save(token=token, username=user_id, user_id=user_id, api_key=key)
-                logger.info("Authentication Successful")
-            else:
+            async def stop_server_once_request_is_done():
+                while not await request.is_disconnected():
+                    sleep(0.25)
+                server.should_exit = True
+
+            if not token:
                 logger.warn(
-                    "Authentication Failed. This is most likely because you're using an older version of the CLI. \n"  # noqa E501
+                    "Login Failed. This is most likely because you're using an older version of the CLI. \n"  # noqa E501
                     "Please try to update the CLI or open an issue with this information \n"  # E501
                     f"expected token in {request.query_params.items()}"
                 )
+                return RedirectResponse(
+                    url=f"{get_lightning_cloud_url()}/cli-login-failed",
+                    background=BackgroundTask(stop_server_once_request_is_done),
+                )
+
+            auth.save(token=token, username=user_id, user_id=user_id, api_key=key)
+            logger.info("Login Successful")
 
             # Include the credentials in the redirect so that UI will also be logged in
             params = urlencode(dict(token=token, key=key, userID=user_id))
 
             return RedirectResponse(
-                url=f"{get_lightning_cloud_url()}/me/apps?{params}",
-                # The response background task is being executed right after the server finished writing the response
-                background=BackgroundTask(stop_server),
+                url=f"{get_lightning_cloud_url()}/cli-login-successful?{params}",
+                background=BackgroundTask(stop_server_once_request_is_done),
             )
 
-        def stop_server():
-            server.should_exit = True
-
         server = uvicorn.Server(config=uvicorn.Config(app, port=port, log_level="error"))
         server.run()