feat(docs): update first_screen content in auth params doc (#768)

docs/docs/references/openid-connect/authentication-parameters/README.md

@@ -9,15 +9,42 @@ In addition to the parameters required by the [OpenID Connect Core specification
 
 ## First screen
 
-<Availability cloud oss={{ major: 1, minor: 15 }} />
+<Availability cloud oss={{ major: 1, minor: 20 }} />
+
+This parameter allows you to customize the first screen that users see when they start the authentication process.
+The value for this parameter can be:
+
+- `sign_in`: Allow users to directly access the sign-in page.
+- `register`: Allow users to directly access the registration page.
+- `single_sign_on`: Allow users to directly access the single sign-on (SSO) page.
+- `identifier:sign_in`: Allow users to direct access a page that only display specific identifier-based sign-in methods to users.
+- `identifier:register`: Allow users to direct access a page that only display specific identifier-based registration methods to users.
+- `reset_password`: Allow users to directly access the password reset page.
+
+If omitted, the default value is `sign_in`.
+
+:::note
+In OSS version, the `first_screen` parameter has been supported since version 1.15.0 for `signIn` and `register`.
+However, now the `signIn` value has been deprecated and should now be replaced with `sign_in`
+:::
+
+You can specify an additional `identifier` parameter to focus the screen on a specific identifier if you're using the following values for the `first_screen` parameter:
 
-This parameter allows you to customize the first screen that users see when they start the authentication process. The value can be `signIn` or `register`. If omitted, the default value is `signIn`.
+- `identifier:sign_in`
+- `identifier:register`
+- `reset_password`
 
-Here's a non-normative example of the authentication request with the `first_screen` parameter:
+Valid `identifier` values are `username`, `email`, and `phone`. Multiple identifiers can be specified by separating them with spaces.
+
+:::note
+Unsupported identifiers in the sign-in experience configuration will be ignored. If all specified identifiers are unsupported, the default sign-in experience configuration will be used. If no identifier is supported in the sign-in experience configuration, the user will be redirected to the sign-in page.
+:::
+
+Below is a non-normative example of an authentication request with the `first_screen` parameter:
 
 ```bash
 curl --location \
-  --request GET 'https://[tenant-id].logto.app/oidc/auth?client_id=1234567890&...&first_screen=register'
+  --request GET 'https://[tenant-id].logto.app/oidc/auth?client_id=1234567890&...&first_screen=identifier:sign_in&identifier=email username'
 ```
 
 :::info
@@ -27,10 +54,19 @@ When `first_screen` is set, the legacy `interaction_mode` parameter is ignored.
 In supported Logto SDKs, you can set the `firstScreen` property when calling the `signIn` method:
 
 ```ts title="JavaScript"
+/* For register screen */
 logtoClient.signIn({
   redirectUri: 'https://your-app.com/callback',
   firstScreen: 'register',
 });
+
+/* For identifier sign-in screen */
+logtoClient.signIn({
+  redirectUri: 'https://your-app.com/callback',
+  firstScreen: 'identifier:sign_in',
+  /* JavaScript SDK using `identifiers` option to specify the `identifier` parameter */
+  identifiers: ['email', 'username'],
+});
 ```
 
 :::note