docs: identifier first authentication

docs/identities/sign-in/two-step-login.mdx

@@ -0,0 +1,33 @@
+---
+id: two-step-login
+title: Two-step login
+sidebar_label: Two-step login
+slug: two-step-login
+---
+
+With a one-step login, when you enable multiple authentication strategies (for example password, code via email, and passkey), the
+identity traits will be repeated for each authentication strategy.
+
+Compare this to a two-step login: Now, the user is prompted for the identity traits in the first step, and asked to choose a
+credential method for authentication next. This results in a more stream-lined user experience.
+
+:::info
+
+Identity traits are data associated with an identity that can be modified by the user. The traits are configured through the
+identity schema.
+
+[Learn more about identity traits](../../kratos/manage-identities/managing-users-identities-metadata#traits)
+
+:::
+
+![Login with two-step login vs one-step login](./_static/two-step-login.png)
+
+To disable the legacy one-step login, go to https://console.ory.sh/projects/current/authentication and switch off "Enable legacy
+one-step login" or use the Ory CLI:
+
+```bash
+ory list projects # to get the project id
+
+ory patch project ${project_id} \
+  --replace '/services/identity/config/selfservice/flows/login/enable_legacy_one_step=false'
+```