Fix links on auth page to sdk/api ref (#1572)

Fixes DOC-391

Author: katmayb

src/langsmith/set-up-custom-auth.mdx

@@ -78,7 +78,7 @@ Now that you have a base LangGraph app, add authentication to it.
 In this tutorial, you will start with a hard-coded token for example purposes. You will get to a "production-ready" authentication scheme in the third tutorial.
 </Note>
 
-The [`Auth`](https://langchain-ai.github.io/langgraph/cloud/reference/sdk/python-sdk_ref#langgraph_sdk.auth.Auth) object lets you register an authentication function that the LangSmith deployment will run on every request. This function receives each request and decides whether to accept or reject.
+The @[Auth] object lets you register an authentication function that the LangSmith deployment will run on every request. This function receives each request and decides whether to accept or reject.
 
 Create a new file `src/security/auth.py`. This is where your code will live to check if users are allowed to access your bot:
 
@@ -114,12 +114,12 @@ async def get_current_user(authorization: str | None) -> Auth.types.MinimalUserD
     }
 ```
 
-Notice that your [authentication](https://langchain-ai.github.io/langgraph/cloud/reference/sdk/python-sdk_ref#langgraph_sdk.auth.Auth.authenticate) handler does two important things:
+Notice that your @[Auth.authenticate] handler does two important things:
 
 1. Checks if a valid token is provided in the request's [Authorization header](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Authorization)
-2. Returns the user's [identity](https://langchain-ai.github.io/langgraph/cloud/reference/sdk/python-sdk_ref#langgraph_sdk.auth.types.MinimalUserDict)
+2. Returns the user's @[MinimalUserDict]
 
-Now tell LangGraph to use authentication by adding the following to the [`langgraph.json`](/langsmith/cli#configuration-file) configuration:
+Now tell LangGraph to use authentication by adding the following to the @[langgraph.json] configuration:
 
 ```json {highlight={7-9}} title="langgraph.json"
 {
@@ -203,4 +203,4 @@ Now that you can control who accesses your bot, you might want to:
 
 1. Continue the tutorial by going to [Make conversations private](/langsmith/resource-auth) to learn about resource authorization.
 2. Read more about [authentication concepts](/langsmith/auth).
-3. Check out the [API reference](https://langchain-ai.github.io/langgraph/cloud/reference/sdk/python-sdk_ref) for more authentication details.
+3. Check out the API reference for @[Auth], @[Auth.authenticate], and @[MinimalUserDict] for more authentication details.