diff --git a/book.toml b/book.toml
index fa1f0cfeb..8d5f2afa4 100644
--- a/book.toml
+++ b/book.toml
@@ -24,3 +24,6 @@ git-repository-url = "https://github.com/element-hq/matrix-authentication-servic
 
 # The path that the docs are hosted on
 site-url = "/matrix-authentication-service/"
+
+[output.html.redirect]
+"/as-login.html" = "setup/migration.html#encrypted-bridges-need-msc4190-support"
diff --git a/docs/SUMMARY.md b/docs/SUMMARY.md
index c638412f2..00cf02461 100644
--- a/docs/SUMMARY.md
+++ b/docs/SUMMARY.md
@@ -48,7 +48,3 @@
 - [Database](./development/database.md)
 - [Cleanup jobs](./development/cleanup-jobs.md)
 - [Internal GraphQL API](./development/graphql.md)
-
----
-
-[Application Services login](./as-login.md)
diff --git a/docs/as-login.md b/docs/as-login.md
deleted file mode 100644
index 0eed4f9e3..000000000
--- a/docs/as-login.md
+++ /dev/null
@@ -1,7 +0,0 @@
-# About Application Services login
-
-Encrypted Application Services/Bridges currently leverage the `m.login.application_service` login type to create devices for users.
-This API is *not* available in the Matrix Authentication Service.
-
-We're working on a solution to support this use case, but in the meantime, this means **encrypted bridges will not work with the Matrix Authentication Service.**
-A workaround is to disable E2EE support in your bridge setup.
diff --git a/docs/setup/migration.md b/docs/setup/migration.md
index 6cd8ce98a..3aa7e8d0c 100644
--- a/docs/setup/migration.md
+++ b/docs/setup/migration.md
@@ -30,6 +30,15 @@ If your Synapse homeserver currently uses a custom password provider module, ple
 It is worth noting that MAS currently only supports PostgreSQL as a database backend.
 The migration tool only supports reading from PostgreSQL for the Synapse database as well.
 
+#### Encrypted bridges need MSC4190 support
+
+Application services used to log in through the legacy `m.login.application_service` login type to create encryption-capable devices for their users.
+This login type is not available once authentication is delegated to MAS: encrypted bridges must instead create devices through the [device management endpoints](https://spec.matrix.org/v1.19/application-service-api/#device-management) introduced by [MSC4190](https://github.com/matrix-org/matrix-spec-proposals/pull/4190).
+
+This requires Synapse 1.141.0 or later, and a bridge which implements MSC4190.
+mautrix-based bridges do, with the `encryption.msc4190` option; see [their documentation](https://docs.mau.fi/bridges/general/end-to-bridge-encryption.html#use-with-next-gen-auth-oauth-mas-msc4190).
+For other bridges, check with their author.
+
 ### Install and configure MAS alongside your existing homeserver
 
 Follow the instructions in the [installation guide](installation.md) to install MAS alongside your existing homeserver.