Update 3pid invite section to reflect signed property

event-schemas/examples/v1/m.room.member

@@ -8,7 +8,15 @@
         "token": "pc98",
         "public_key": "abc123",
         "key_validity_url": "https://magic.forest/verifykey",
-        "signature": "q1w2e3",
+        "signed": {
+          "mxid": "@alice:localhost",
+          "token": "pc98",
+          "signatures": {
+            "magic.forest": {
+              "ed25519:0": "poi098"
+            }
+          }
+        },
         "sender": "@zun:zun.soft"
     }
   },

event-schemas/schema/v1/m.room.member

@@ -38,9 +38,23 @@
                             "type": "string",
                             "description": "A base64-encoded ed25519 key with which token must be signed."
                         },
-                        "signature": {
+                        "signed": {
-                            "type": "string",
+                            "type": "object",
-                            "description": "A base64-encoded signature of token with public_key."
+                            "title": "signed_third_party_invite",
+                            "properties": {
+                                "mxid": {
+                                    "type": "string",
+                                    "description": "The invited matrix user ID. Must be equal to the user_id property of the event."
+                                },
+                                "token": {
+                                    "type": "string",
+                                    "description": "The token property of the containing third_party_invite object.",
+                                },
+                                "signatures": {
+                                    "type": "object",
+                                    "description": "A single signature from the verifying server, in the format specified by the Signing Events section."
+                                }
+                            }
                         },
                         "sender": {
                             "type": "string",

specification/modules/third_party_invites.rst

@@ -36,7 +36,8 @@ A client asks a server to invite a user by their third party identifier.
 Server behaviour
 ----------------
 
-All homeservers MUST verify that sig(``token``, ``public_key``) = ``signature``.
+All homeservers MUST verify the signature in the ``signed`` property of the
+``third_party_invite`` property in the ``content`` the event.
 
 If a client of the current homeserver is joining by an
 ``m.room.third_party_invite``, that homesever MUST validate that the public
@@ -93,11 +94,12 @@ For example:
     When the third party user validates their identity, they are told about the
     invite, and ask their homeserver, H3, to join the room.
 
-    H3 validates that sign(``token``, ``public_key``) = ``signature``, and may check
+    H3 validates that signature in the ``signed`` property of the
-    ``key_validity_url``.
+    ``third_party_invite`` property of the ``content`` property of the  event,
+    and may check ``key_validity_url``.
 
-    H3 then asks H1 to join it to the room. H1 *must* validate that
+    H3 then asks H1 to join it to the room. H1 *must* validate the ``signed``
-    sign(``token``, ``public_key``) = ``signature`` *and* check ``key_validity_url``.
+    property *and* check ``key_validity_url``.
 
     Having validated these things, H1 writes the join event to the room, and H3
     begins participating in the room. H2 *must* accept this event.