message: update docs for ProxiedSignInPage
diff: @@ -150,6 +150,31 @@ const app = createApp({
  });
  ```
  +If the provider in auth backend expects additional headers such as `x-provider-token`, there is now a way to configure that in `ProxiedSignInPage` using the optional `headers` prop.
  +
  +Example:
  +
  +```tsx
  +<ProxiedSignInPage
  + {...props}
  + provider="my-custom-provider"
  + headers={{ 'x-some-key': someValue }}
  +/>
  +```
  +
  +Headers can also be returned in an async manner:
  +
  +```tsx
  +<ProxiedSignInPage
  + {...props}
  + provider="my-custom-provider"
  + headers={async () => {
  + const someValue = await someFn();
  + return { 'x-some-key': someValue };
  + }}
  +/>
  +```
  +
  A downside of this method is that it can be cumbersome to set up for local development.
  As a workaround for this, it's possible to dynamically select the sign-in page based on
  what environment the app is running in, and then use a different sign-in method for local
  