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docs/restrict-hs.md

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+# Restricting available homeserver
+
+If you want to have your Synapse Admin instance work only with specific homeserver(-s),
+you can do that by setting `restrictBaseUrl` in the configuration.
+
+## Configuration
+
+You can do that for a single homeserver or multiple homeservers at once, as `restrictBaseUrl` accepts both a string and
+an array of strings.
+
+The examples below contain the configuration settings to restrict the Synapse Admin instance to work only with
+`example.com` (with Synapse runing at `matrix.example.com`) and
+`example.net` (with Synapse running at `synapse.example.net`) homeservers.
+Note that the homeserver URL should be the _actual_ homeserver URL, and not the delegated one.
+
+So, if you have a homeserver `example.com` where users have MXIDs like `@user:example.com`,
+but actual Synapse is installed on `matrix.example.com` subdomain, you should use `https://matrix.example.com` in the
+configuration.
+
+### config.json
+
+```json
+{
+  "restrictBaseUrl": [
+    "https://matrix.example.com",
+    "https://synapse.example.net"
+  ]
+}
+```
+
+### `/.well-known/matrix/client`
+
+```json
+{
+  "cc.etke.synapse-admin": {
+    "restrictBaseUrl": [
+      "https://matrix.example.com",
+      "https://synapse.example.net"
+    ]
+  }
+}
+```