diff --git a/authstate.go b/authstate.go
index f512275a..15de09b4 100644
--- a/authstate.go
+++ b/authstate.go
@@ -17,10 +17,10 @@ type StateProvider interface {
 
 type FederatedStateClient interface {
 	LookupState(
-		ctx context.Context, s ServerName, roomID, eventID string, roomVersion RoomVersion,
+		ctx context.Context, origin, s ServerName, roomID, eventID string, roomVersion RoomVersion,
 	) (res RespState, err error)
 	LookupStateIDs(
-		ctx context.Context, s ServerName, roomID, eventID string,
+		ctx context.Context, origin, s ServerName, roomID, eventID string,
 	) (res RespStateIDs, err error)
 }
 
@@ -28,6 +28,7 @@ type FederatedStateClient interface {
 type FederatedStateProvider struct {
 	FedClient FederatedStateClient
 	// The remote server to ask.
+	Origin ServerName
 	Server ServerName
 	// Set to true to remember the auth event IDs for the room at various states
 	RememberAuthEvents bool
@@ -38,7 +39,7 @@ type FederatedStateProvider struct {
 
 // StateIDsBeforeEvent implements StateProvider
 func (p *FederatedStateProvider) StateIDsBeforeEvent(ctx context.Context, event *HeaderedEvent) ([]string, error) {
-	res, err := p.FedClient.LookupStateIDs(ctx, p.Server, event.RoomID(), event.EventID())
+	res, err := p.FedClient.LookupStateIDs(ctx, p.Origin, p.Server, event.RoomID(), event.EventID())
 	if err != nil {
 		return nil, err
 	}
@@ -50,7 +51,7 @@ func (p *FederatedStateProvider) StateIDsBeforeEvent(ctx context.Context, event
 
 // StateBeforeEvent implements StateProvider
 func (p *FederatedStateProvider) StateBeforeEvent(ctx context.Context, roomVer RoomVersion, event *HeaderedEvent, eventIDs []string) (map[string]*Event, error) {
-	res, err := p.FedClient.LookupState(ctx, p.Server, event.RoomID(), event.EventID(), roomVer)
+	res, err := p.FedClient.LookupState(ctx, p.Origin, p.Server, event.RoomID(), event.EventID(), roomVer)
 	if err != nil {
 		return nil, err
 	}
diff --git a/backfill.go b/backfill.go
index 5fa3ea36..a1e50ca8 100644
--- a/backfill.go
+++ b/backfill.go
@@ -10,7 +10,7 @@ import (
 type BackfillClient interface {
 	// Backfill performs a backfill request to the given server.
 	// https://matrix.org/docs/spec/server_server/latest#get-matrix-federation-v1-backfill-roomid
-	Backfill(ctx context.Context, server ServerName, roomID string, limit int, fromEventIDs []string) (Transaction, error)
+	Backfill(ctx context.Context, origin, server ServerName, roomID string, limit int, fromEventIDs []string) (Transaction, error)
 }
 
 // BackfillRequester contains the necessary functions to perform backfill requests from one server to another.
@@ -45,7 +45,7 @@ type BackfillRequester interface {
 // but to verify it we need to know the prev_events of fromEventIDs.
 //
 // TODO: When does it make sense to return errors?
-func RequestBackfill(ctx context.Context, b BackfillRequester, keyRing JSONVerifier,
+func RequestBackfill(ctx context.Context, origin ServerName, b BackfillRequester, keyRing JSONVerifier,
 	roomID string, ver RoomVersion, fromEventIDs []string, limit int) ([]*HeaderedEvent, error) {
 
 	if len(fromEventIDs) == 0 {
@@ -67,7 +67,7 @@ func RequestBackfill(ctx context.Context, b BackfillRequester, keyRing JSONVerif
 			return nil, fmt.Errorf("gomatrixserverlib: RequestBackfill context cancelled %w", ctx.Err())
 		}
 		// fetch some events, and try a different server if it fails
-		txn, err := b.Backfill(ctx, s, roomID, limit, fromEventIDs)
+		txn, err := b.Backfill(ctx, origin, s, roomID, limit, fromEventIDs)
 		if err != nil {
 			continue // try the next server
 		}
diff --git a/backfill_test.go b/backfill_test.go
index 48e055a3..4b0eb9b9 100644
--- a/backfill_test.go
+++ b/backfill_test.go
@@ -12,7 +12,7 @@ import (
 
 type testBackfillRequester struct {
 	servers                         []ServerName
-	backfillFn                      func(server ServerName, roomID string, fromEventIDs []string, limit int) (*Transaction, error)
+	backfillFn                      func(origin, server ServerName, roomID string, fromEventIDs []string, limit int) (*Transaction, error)
 	authEventsToProvide             [][]byte
 	stateIDsAtEvent                 map[string][]string
 	callOrderForStateIDsBeforeEvent []string // event IDs called
@@ -28,8 +28,8 @@ func (t *testBackfillRequester) StateBeforeEvent(ctx context.Context, roomVer Ro
 func (t *testBackfillRequester) ServersAtEvent(ctx context.Context, roomID, eventID string) []ServerName {
 	return t.servers
 }
-func (t *testBackfillRequester) Backfill(ctx context.Context, server ServerName, roomID string, limit int, fromEventIDs []string) (Transaction, error) {
-	txn, err := t.backfillFn(server, roomID, fromEventIDs, limit)
+func (t *testBackfillRequester) Backfill(ctx context.Context, origin, server ServerName, roomID string, limit int, fromEventIDs []string) (Transaction, error) {
+	txn, err := t.backfillFn(origin, server, roomID, fromEventIDs, limit)
 	if err != nil {
 		return Transaction{}, err
 	}
@@ -92,14 +92,14 @@ func TestRequestBackfillMultipleServers(t *testing.T) {
 			"$fnwGrQEpiOIUoDU2:baba.is.you": {"$WCraVpPZe5TtHAqs:baba.is.you"},
 			"$WCraVpPZe5TtHAqs:baba.is.you": nil,
 		},
-		backfillFn: func(server ServerName, roomID string, fromEventIDs []string, limit int) (*Transaction, error) {
+		backfillFn: func(origin, server ServerName, roomID string, fromEventIDs []string, limit int) (*Transaction, error) {
 			if roomID != testRoomID {
 				return nil, fmt.Errorf("bad room id: %s", roomID)
 			}
 			if server == serverA {
 				// server A returns events 1 and 3.
 				return &Transaction{
-					Origin:         serverA,
+					Origin:         origin,
 					OriginServerTS: AsTimestamp(time.Now()),
 					PDUs: []json.RawMessage{
 						testBackfillEvents[1], testBackfillEvents[3],
@@ -108,7 +108,7 @@ func TestRequestBackfillMultipleServers(t *testing.T) {
 			} else if server == serverB {
 				// server B returns events 0 and 2 and 3.
 				return &Transaction{
-					Origin:         serverB,
+					Origin:         origin,
 					OriginServerTS: AsTimestamp(time.Now()),
 					PDUs: []json.RawMessage{
 						testBackfillEvents[0], testBackfillEvents[2], testBackfillEvents[3],
@@ -118,7 +118,7 @@ func TestRequestBackfillMultipleServers(t *testing.T) {
 			return nil, fmt.Errorf("bad server name: %s", server)
 		},
 	}
-	result, err := RequestBackfill(ctx, tbr, keyRing, testRoomID, RoomVersionV1, testFromEventIDs, testLimit)
+	result, err := RequestBackfill(ctx, serverA, tbr, keyRing, testRoomID, RoomVersionV1, testFromEventIDs, testLimit)
 	if err != nil {
 		t.Fatalf("RequestBackfill got error: %s", err)
 	}
@@ -157,13 +157,13 @@ func TestRequestBackfillTopologicalSort(t *testing.T) {
 			"$fnwGrQEpiOIUoDU2:baba.is.you": {"$WCraVpPZe5TtHAqs:baba.is.you"},
 			"$WCraVpPZe5TtHAqs:baba.is.you": nil,
 		},
-		backfillFn: func(server ServerName, roomID string, fromEventIDs []string, limit int) (*Transaction, error) {
+		backfillFn: func(origin, server ServerName, roomID string, fromEventIDs []string, limit int) (*Transaction, error) {
 			if roomID != testRoomID {
 				return nil, fmt.Errorf("bad room id: %s", roomID)
 			}
 			if server == serverA {
 				return &Transaction{
-					Origin:         serverA,
+					Origin:         origin,
 					OriginServerTS: AsTimestamp(time.Now()),
 					PDUs: []json.RawMessage{
 						testBackfillEvents[0], testBackfillEvents[1], testBackfillEvents[2], testBackfillEvents[3],
@@ -173,7 +173,7 @@ func TestRequestBackfillTopologicalSort(t *testing.T) {
 			return nil, fmt.Errorf("bad server name: %s", server)
 		},
 	}
-	result, err := RequestBackfill(ctx, tbr, keyRing, testRoomID, RoomVersionV1, testFromEventIDs, testLimit)
+	result, err := RequestBackfill(ctx, serverA, tbr, keyRing, testRoomID, RoomVersionV1, testFromEventIDs, testLimit)
 	if err != nil {
 		t.Fatalf("RequestBackfill got error: %s", err)
 	}
diff --git a/federationclient.go b/federationclient.go
index 4b47231c..b8b6279b 100644
--- a/federationclient.go
+++ b/federationclient.go
@@ -16,9 +16,13 @@ import (
 // "Authorization: X-Matrix" headers to requests that need ed25519 signatures
 type FederationClient struct {
 	Client
-	serverName       ServerName
-	serverKeyID      KeyID
-	serverPrivateKey ed25519.PrivateKey
+	identities []*SigningIdentity
+}
+
+type SigningIdentity struct {
+	ServerName ServerName
+	KeyID      KeyID
+	PrivateKey ed25519.PrivateKey
 }
 
 // NewFederationClient makes a new FederationClient. You can supply
@@ -26,21 +30,29 @@ type FederationClient struct {
 // TLS validation etc - see WithTransport, WithTimeout, WithSkipVerify,
 // WithDNSCache etc.
 func NewFederationClient(
-	serverName ServerName, keyID KeyID, privateKey ed25519.PrivateKey,
+	identities []*SigningIdentity,
 	options ...ClientOption,
 ) *FederationClient {
 	return &FederationClient{
 		Client: *NewClient(
 			append(options, WithWellKnownSRVLookups(true))...,
 		),
-		serverName:       serverName,
-		serverKeyID:      keyID,
-		serverPrivateKey: privateKey,
+		identities: append([]*SigningIdentity{}, identities...),
 	}
 }
 
 func (ac *FederationClient) doRequest(ctx context.Context, r FederationRequest, resBody interface{}) error {
-	if err := r.Sign(ac.serverName, ac.serverKeyID, ac.serverPrivateKey); err != nil {
+	var identity *SigningIdentity
+	for _, id := range ac.identities {
+		if id.ServerName == r.fields.Origin {
+			identity = id
+			break
+		}
+	}
+	if identity == nil {
+		return fmt.Errorf("no signing identity for server name %q", r.fields.Origin)
+	}
+	if err := r.Sign(identity.ServerName, identity.KeyID, identity.PrivateKey); err != nil {
 		return err
 	}
 
@@ -60,7 +72,7 @@ func (ac *FederationClient) SendTransaction(
 	ctx context.Context, t Transaction,
 ) (res RespSend, err error) {
 	path := federationPathPrefixV1 + "/send/" + string(t.TransactionID)
-	req := NewFederationRequest("PUT", t.Destination, path)
+	req := NewFederationRequest("PUT", t.Origin, t.Destination, path)
 	if err = req.SetContent(t); err != nil {
 		return
 	}
@@ -93,14 +105,14 @@ func makeVersionQueryString(roomVersions []RoomVersion) string {
 // server's key and pass it to SendJoin.
 // See https://matrix.org/docs/spec/server_server/unstable.html#joining-rooms
 func (ac *FederationClient) MakeJoin(
-	ctx context.Context, s ServerName, roomID, userID string,
+	ctx context.Context, origin, s ServerName, roomID, userID string,
 	roomVersions []RoomVersion,
 ) (res RespMakeJoin, err error) {
 	versionQueryString := makeVersionQueryString(roomVersions)
 	path := federationPathPrefixV1 + "/make_join/" +
 		url.PathEscape(roomID) + "/" +
 		url.PathEscape(userID) + versionQueryString
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -110,9 +122,9 @@ func (ac *FederationClient) MakeJoin(
 // This is used to join a room the local server isn't a member of.
 // See https://matrix.org/docs/spec/server_server/unstable.html#joining-rooms
 func (ac *FederationClient) SendJoin(
-	ctx context.Context, s ServerName, event *Event,
+	ctx context.Context, origin, s ServerName, event *Event,
 ) (res RespSendJoin, err error) {
-	return ac.sendJoin(ctx, s, event, false)
+	return ac.sendJoin(ctx, origin, s, event, false)
 }
 
 // SendJoinPartialState sends a join m.room.member event obtained using MakeJoin via a
@@ -121,14 +133,14 @@ func (ac *FederationClient) SendJoin(
 // This is used to join a room the local server isn't a member of.
 // See https://matrix.org/docs/spec/server_server/unstable.html#joining-rooms
 func (ac *FederationClient) SendJoinPartialState(
-	ctx context.Context, s ServerName, event *Event,
+	ctx context.Context, origin, s ServerName, event *Event,
 ) (res RespSendJoin, err error) {
-	return ac.sendJoin(ctx, s, event, true)
+	return ac.sendJoin(ctx, origin, s, event, true)
 }
 
 // sendJoin is an internal implementation shared between SendJoin and SendJoinPartialState
 func (ac *FederationClient) sendJoin(
-	ctx context.Context, s ServerName, event *Event, partialState bool,
+	ctx context.Context, origin, s ServerName, event *Event, partialState bool,
 ) (res RespSendJoin, err error) {
 	path := federationPathPrefixV2 + "/send_join/" +
 		url.PathEscape(event.RoomID()) + "/" +
@@ -137,7 +149,7 @@ func (ac *FederationClient) sendJoin(
 		path += "?org.matrix.msc3706.partial_state=true"
 	}
 
-	req := NewFederationRequest("PUT", s, path)
+	req := NewFederationRequest("PUT", origin, s, path)
 	if err = req.SetContent(event); err != nil {
 		return
 	}
@@ -148,7 +160,7 @@ func (ac *FederationClient) sendJoin(
 		v1path := federationPathPrefixV1 + "/send_join/" +
 			url.PathEscape(event.RoomID()) + "/" +
 			url.PathEscape(event.EventID())
-		v1req := NewFederationRequest("PUT", s, v1path)
+		v1req := NewFederationRequest("PUT", origin, s, v1path)
 		if err = v1req.SetContent(event); err != nil {
 			return
 		}
@@ -170,14 +182,14 @@ func (ac *FederationClient) sendJoin(
 // server's key and pass it to SendKnock.
 // See https://spec.matrix.org/v1.3/server-server-api/#knocking-upon-a-room
 func (ac *FederationClient) MakeKnock(
-	ctx context.Context, s ServerName, roomID, userID string,
+	ctx context.Context, origin, s ServerName, roomID, userID string,
 	roomVersions []RoomVersion,
 ) (res RespMakeKnock, err error) {
 	versionQueryString := makeVersionQueryString(roomVersions)
 	path := federationPathPrefixV1 + "/make_knock/" +
 		url.PathEscape(roomID) + "/" +
 		url.PathEscape(userID) + versionQueryString
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -187,13 +199,13 @@ func (ac *FederationClient) MakeKnock(
 // This is used to ask to join a room the local server isn't a member of.
 // See https://spec.matrix.org/v1.3/server-server-api/#knocking-upon-a-room
 func (ac *FederationClient) SendKnock(
-	ctx context.Context, s ServerName, event *Event,
+	ctx context.Context, origin, s ServerName, event *Event,
 ) (res RespSendKnock, err error) {
 	path := federationPathPrefixV1 + "/send_knock/" +
 		url.PathEscape(event.RoomID()) + "/" +
 		url.PathEscape(event.EventID())
 
-	req := NewFederationRequest("PUT", s, path)
+	req := NewFederationRequest("PUT", origin, s, path)
 	if err = req.SetContent(event); err != nil {
 		return
 	}
@@ -207,12 +219,12 @@ func (ac *FederationClient) SendKnock(
 // the event_id with our own, and pass it to SendLeave.
 // See https://matrix.org/docs/spec/server_server/r0.1.1.html#get-matrix-federation-v1-make-leave-roomid-userid
 func (ac *FederationClient) MakeLeave(
-	ctx context.Context, s ServerName, roomID, userID string,
+	ctx context.Context, origin, s ServerName, roomID, userID string,
 ) (res RespMakeLeave, err error) {
 	path := federationPathPrefixV1 + "/make_leave/" +
 		url.PathEscape(roomID) + "/" +
 		url.PathEscape(userID)
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -222,12 +234,12 @@ func (ac *FederationClient) MakeLeave(
 // This is used to reject a remote invite.
 // See https://matrix.org/docs/spec/server_server/r0.1.1.html#put-matrix-federation-v1-send-leave-roomid-eventid
 func (ac *FederationClient) SendLeave(
-	ctx context.Context, s ServerName, event *Event,
+	ctx context.Context, origin, s ServerName, event *Event,
 ) (err error) {
 	path := federationPathPrefixV2 + "/send_leave/" +
 		url.PathEscape(event.RoomID()) + "/" +
 		url.PathEscape(event.EventID())
-	req := NewFederationRequest("PUT", s, path)
+	req := NewFederationRequest("PUT", origin, s, path)
 	if err = req.SetContent(event); err != nil {
 		return
 	}
@@ -239,7 +251,7 @@ func (ac *FederationClient) SendLeave(
 		v1path := federationPathPrefixV1 + "/send_leave/" +
 			url.PathEscape(event.RoomID()) + "/" +
 			url.PathEscape(event.EventID())
-		v1req := NewFederationRequest("PUT", s, v1path)
+		v1req := NewFederationRequest("PUT", origin, s, v1path)
 		if err = v1req.SetContent(event); err != nil {
 			return
 		}
@@ -255,12 +267,12 @@ func (ac *FederationClient) SendLeave(
 // SendInvite sends an invite m.room.member event to an invited server to be
 // signed by it. This is used to invite a user that is not on the local server.
 func (ac *FederationClient) SendInvite(
-	ctx context.Context, s ServerName, event *Event,
+	ctx context.Context, origin, s ServerName, event *Event,
 ) (res RespInvite, err error) {
 	path := federationPathPrefixV1 + "/invite/" +
 		url.PathEscape(event.RoomID()) + "/" +
 		url.PathEscape(event.EventID())
-	req := NewFederationRequest("PUT", s, path)
+	req := NewFederationRequest("PUT", origin, s, path)
 	if err = req.SetContent(event); err != nil {
 		return
 	}
@@ -271,13 +283,13 @@ func (ac *FederationClient) SendInvite(
 // SendInviteV2 sends an invite m.room.member event to an invited server to be
 // signed by it. This is used to invite a user that is not on the local server.
 func (ac *FederationClient) SendInviteV2(
-	ctx context.Context, s ServerName, request InviteV2Request,
+	ctx context.Context, origin, s ServerName, request InviteV2Request,
 ) (res RespInviteV2, err error) {
 	event := request.Event()
 	path := federationPathPrefixV2 + "/invite/" +
 		url.PathEscape(event.RoomID()) + "/" +
 		url.PathEscape(event.EventID())
-	req := NewFederationRequest("PUT", s, path)
+	req := NewFederationRequest("PUT", origin, s, path)
 	if err = req.SetContent(request); err != nil {
 		return
 	}
@@ -287,7 +299,7 @@ func (ac *FederationClient) SendInviteV2(
 	if ok && gerr.Code == 404 {
 		// fallback to v1 which returns [200, body]
 		var resp RespInvite
-		resp, err = ac.SendInvite(ctx, s, request.Event())
+		resp, err = ac.SendInvite(ctx, origin, s, request.Event())
 		if err != nil {
 			return
 		}
@@ -306,11 +318,11 @@ func (ac *FederationClient) SendInviteV2(
 // This is used to exchange a m.room.third_party_invite event for a m.room.member
 // one in a room the local server isn't a member of.
 func (ac *FederationClient) ExchangeThirdPartyInvite(
-	ctx context.Context, s ServerName, builder EventBuilder,
+	ctx context.Context, origin, s ServerName, builder EventBuilder,
 ) (err error) {
 	path := federationPathPrefixV1 + "/exchange_third_party_invite/" +
 		url.PathEscape(builder.RoomID)
-	req := NewFederationRequest("PUT", s, path)
+	req := NewFederationRequest("PUT", origin, s, path)
 	if err = req.SetContent(builder); err != nil {
 		return
 	}
@@ -322,13 +334,13 @@ func (ac *FederationClient) ExchangeThirdPartyInvite(
 // LookupState retrieves the room state for a room at an event from a
 // remote matrix server as full matrix events.
 func (ac *FederationClient) LookupState(
-	ctx context.Context, s ServerName, roomID, eventID string, roomVersion RoomVersion,
+	ctx context.Context, origin, s ServerName, roomID, eventID string, roomVersion RoomVersion,
 ) (res RespState, err error) {
 	path := federationPathPrefixV1 + "/state/" +
 		url.PathEscape(roomID) +
 		"?event_id=" +
 		url.QueryEscape(eventID)
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -336,13 +348,13 @@ func (ac *FederationClient) LookupState(
 // LookupStateIDs retrieves the room state for a room at an event from a
 // remote matrix server as lists of matrix event IDs.
 func (ac *FederationClient) LookupStateIDs(
-	ctx context.Context, s ServerName, roomID, eventID string,
+	ctx context.Context, origin, s ServerName, roomID, eventID string,
 ) (res RespStateIDs, err error) {
 	path := federationPathPrefixV1 + "/state_ids/" +
 		url.PathEscape(roomID) +
 		"?event_id=" +
 		url.QueryEscape(eventID)
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -351,12 +363,12 @@ func (ac *FederationClient) LookupStateIDs(
 // given bracket.
 // https://matrix.org/docs/spec/server_server/r0.1.3#post-matrix-federation-v1-get-missing-events-roomid
 func (ac *FederationClient) LookupMissingEvents(
-	ctx context.Context, s ServerName, roomID string,
+	ctx context.Context, origin, s ServerName, roomID string,
 	missing MissingEvents, roomVersion RoomVersion,
 ) (res RespMissingEvents, err error) {
 	path := federationPathPrefixV1 + "/get_missing_events/" +
 		url.PathEscape(roomID)
-	req := NewFederationRequest("POST", s, path)
+	req := NewFederationRequest("POST", origin, s, path)
 	if err = req.SetContent(missing); err != nil {
 		return
 	}
@@ -366,7 +378,7 @@ func (ac *FederationClient) LookupMissingEvents(
 
 // Peek starts a peek on a remote server: see MSC2753
 func (ac *FederationClient) Peek(
-	ctx context.Context, s ServerName, roomID, peekID string,
+	ctx context.Context, origin, s ServerName, roomID, peekID string,
 	roomVersions []RoomVersion,
 ) (res RespPeek, err error) {
 	versionQueryString := ""
@@ -380,7 +392,7 @@ func (ac *FederationClient) Peek(
 	path := federationPathPrefixV1 + "/peek/" +
 		url.PathEscape(roomID) + "/" +
 		url.PathEscape(peekID) + versionQueryString
-	req := NewFederationRequest("PUT", s, path)
+	req := NewFederationRequest("PUT", origin, s, path)
 	var empty struct{}
 	if err = req.SetContent(empty); err != nil {
 		return
@@ -395,11 +407,11 @@ func (ac *FederationClient) Peek(
 // If the room alias doesn't exist on the remote server then a 404 gomatrix.HTTPError
 // is returned.
 func (ac *FederationClient) LookupRoomAlias(
-	ctx context.Context, s ServerName, roomAlias string,
+	ctx context.Context, origin, s ServerName, roomAlias string,
 ) (res RespDirectory, err error) {
 	path := federationPathPrefixV1 + "/query/directory?room_alias=" +
 		url.QueryEscape(roomAlias)
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -408,10 +420,10 @@ func (ac *FederationClient) LookupRoomAlias(
 // Spec: https://matrix.org/docs/spec/server_server/r0.1.1.html#get-matrix-federation-v1-publicrooms
 // thirdPartyInstanceID can only be non-empty if includeAllNetworks is false.
 func (ac *FederationClient) GetPublicRooms(
-	ctx context.Context, s ServerName, limit int, since string,
+	ctx context.Context, origin, s ServerName, limit int, since string,
 	includeAllNetworks bool, thirdPartyInstanceID string,
 ) (res RespPublicRooms, err error) {
-	return ac.GetPublicRoomsFiltered(ctx, s, limit, since, "", includeAllNetworks, thirdPartyInstanceID)
+	return ac.GetPublicRoomsFiltered(ctx, origin, s, limit, since, "", includeAllNetworks, thirdPartyInstanceID)
 }
 
 // searchTerm is used when querying e.g. remote public rooms
@@ -432,7 +444,7 @@ type postPublicRoomsReq struct {
 // Spec: https://spec.matrix.org/v1.1/server-server-api/#post_matrixfederationv1publicrooms
 // thirdPartyInstanceID can only be non-empty if includeAllNetworks is false.
 func (ac *FederationClient) GetPublicRoomsFiltered(
-	ctx context.Context, s ServerName, limit int, since, filter string,
+	ctx context.Context, origin, s ServerName, limit int, since, filter string,
 	includeAllNetworks bool, thirdPartyInstanceID string,
 ) (res RespPublicRooms, err error) {
 	if includeAllNetworks && thirdPartyInstanceID != "" {
@@ -447,7 +459,7 @@ func (ac *FederationClient) GetPublicRoomsFiltered(
 		Since:                since,
 	}
 	path := federationPathPrefixV1 + "/publicRooms"
-	req := NewFederationRequest("POST", s, path)
+	req := NewFederationRequest("POST", origin, s, path)
 	if err = req.SetContent(roomsReq); err != nil {
 		return
 	}
@@ -461,14 +473,14 @@ func (ac *FederationClient) GetPublicRoomsFiltered(
 // which field of the profile should be returned.
 // Spec: https://matrix.org/docs/spec/server_server/r0.1.1.html#get-matrix-federation-v1-query-profile
 func (ac *FederationClient) LookupProfile(
-	ctx context.Context, s ServerName, userID string, field string,
+	ctx context.Context, origin, s ServerName, userID string, field string,
 ) (res RespProfile, err error) {
 	path := federationPathPrefixV1 + "/query/profile?user_id=" +
 		url.QueryEscape(userID)
 	if field != "" {
 		path += "&field=" + url.QueryEscape(field)
 	}
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -483,9 +495,9 @@ func (ac *FederationClient) LookupProfile(
 //	}
 //
 // https://matrix.org/docs/spec/server_server/latest#post-matrix-federation-v1-user-keys-claim
-func (ac *FederationClient) ClaimKeys(ctx context.Context, s ServerName, oneTimeKeys map[string]map[string]string) (res RespClaimKeys, err error) {
+func (ac *FederationClient) ClaimKeys(ctx context.Context, origin, s ServerName, oneTimeKeys map[string]map[string]string) (res RespClaimKeys, err error) {
 	path := federationPathPrefixV1 + "/user/keys/claim"
-	req := NewFederationRequest("POST", s, path)
+	req := NewFederationRequest("POST", origin, s, path)
 	if err = req.SetContent(map[string]interface{}{
 		"one_time_keys": oneTimeKeys,
 	}); err != nil {
@@ -497,9 +509,9 @@ func (ac *FederationClient) ClaimKeys(ctx context.Context, s ServerName, oneTime
 
 // QueryKeys queries E2E device keys from a remote server.
 // https://matrix.org/docs/spec/server_server/latest#post-matrix-federation-v1-user-keys-query
-func (ac *FederationClient) QueryKeys(ctx context.Context, s ServerName, keys map[string][]string) (res RespQueryKeys, err error) {
+func (ac *FederationClient) QueryKeys(ctx context.Context, origin, s ServerName, keys map[string][]string) (res RespQueryKeys, err error) {
 	path := federationPathPrefixV1 + "/user/keys/query"
-	req := NewFederationRequest("POST", s, path)
+	req := NewFederationRequest("POST", origin, s, path)
 	if err = req.SetContent(map[string]interface{}{
 		"device_keys": keys,
 	}); err != nil {
@@ -512,10 +524,10 @@ func (ac *FederationClient) QueryKeys(ctx context.Context, s ServerName, keys ma
 // GetEvent gets an event by ID from a remote server.
 // See https://matrix.org/docs/spec/server_server/r0.1.1.html#get-matrix-federation-v1-event-eventid
 func (ac *FederationClient) GetEvent(
-	ctx context.Context, s ServerName, eventID string,
+	ctx context.Context, origin, s ServerName, eventID string,
 ) (res Transaction, err error) {
 	path := federationPathPrefixV1 + "/event/" + url.PathEscape(eventID)
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -523,10 +535,10 @@ func (ac *FederationClient) GetEvent(
 // GetEventAuth gets an event auth chain from a remote server.
 // See https://matrix.org/docs/spec/server_server/latest#get-matrix-federation-v1-event-auth-roomid-eventid
 func (ac *FederationClient) GetEventAuth(
-	ctx context.Context, s ServerName, roomVersion RoomVersion, roomID, eventID string,
+	ctx context.Context, origin, s ServerName, roomVersion RoomVersion, roomID, eventID string,
 ) (res RespEventAuth, err error) {
 	path := federationPathPrefixV1 + "/event_auth/" + url.PathEscape(roomID) + "/" + url.PathEscape(eventID)
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -534,10 +546,10 @@ func (ac *FederationClient) GetEventAuth(
 // GetUserDevices returns a list of the user's devices from a remote server.
 // See https://matrix.org/docs/spec/server_server/latest#get-matrix-federation-v1-user-devices-userid
 func (ac *FederationClient) GetUserDevices(
-	ctx context.Context, s ServerName, userID string,
+	ctx context.Context, origin, s ServerName, userID string,
 ) (res RespUserDevices, err error) {
 	path := federationPathPrefixV1 + "/user/devices/" + url.PathEscape(userID)
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
@@ -546,7 +558,7 @@ func (ac *FederationClient) GetUserDevices(
 // local database.
 // See https://matrix.org/docs/spec/server_server/unstable.html#get-matrix-federation-v1-backfill-roomid
 func (ac *FederationClient) Backfill(
-	ctx context.Context, s ServerName, roomID string, limit int, eventIDs []string,
+	ctx context.Context, origin, s ServerName, roomID string, limit int, eventIDs []string,
 ) (res Transaction, err error) {
 	// Parse the limit into a string so that we can include it in the URL's query.
 	limitStr := strconv.Itoa(limit)
@@ -564,17 +576,17 @@ func (ac *FederationClient) Backfill(
 	path := u.RequestURI()
 
 	// Send the request.
-	req := NewFederationRequest("GET", s, path)
+	req := NewFederationRequest("GET", origin, s, path)
 	err = ac.doRequest(ctx, req, &res)
 	return
 }
 
 // MSC2836EventRelationships performs an MSC2836 /event_relationships request.
 func (ac *FederationClient) MSC2836EventRelationships(
-	ctx context.Context, dst ServerName, r MSC2836EventRelationshipsRequest, roomVersion RoomVersion,
+	ctx context.Context, origin, dst ServerName, r MSC2836EventRelationshipsRequest, roomVersion RoomVersion,
 ) (res MSC2836EventRelationshipsResponse, err error) {
 	path := "/_matrix/federation/unstable/event_relationships"
-	req := NewFederationRequest("POST", dst, path)
+	req := NewFederationRequest("POST", origin, dst, path)
 	if err = req.SetContent(r); err != nil {
 		return
 	}
@@ -583,13 +595,13 @@ func (ac *FederationClient) MSC2836EventRelationships(
 }
 
 func (ac *FederationClient) MSC2946Spaces(
-	ctx context.Context, dst ServerName, roomID string, suggestedOnly bool,
+	ctx context.Context, origin, dst ServerName, roomID string, suggestedOnly bool,
 ) (res MSC2946SpacesResponse, err error) {
 	path := "/_matrix/federation/v1/hierarchy/" + url.PathEscape(roomID)
 	if suggestedOnly {
 		path += "?suggested_only=true"
 	}
-	req := NewFederationRequest("GET", dst, path)
+	req := NewFederationRequest("GET", origin, dst, path)
 	err = ac.doRequest(ctx, req, &res)
 	if err != nil {
 		gerr, ok := err.(gomatrix.HTTPError)
@@ -599,7 +611,7 @@ func (ac *FederationClient) MSC2946Spaces(
 			if suggestedOnly {
 				path += "?suggested_only=true"
 			}
-			req := NewFederationRequest("GET", dst, path)
+			req := NewFederationRequest("GET", origin, dst, path)
 			err = ac.doRequest(ctx, req, &res)
 		}
 	}
diff --git a/federationclient_test.go b/federationclient_test.go
index dd0b7775..c9bb0c63 100644
--- a/federationclient_test.go
+++ b/federationclient_test.go
@@ -46,7 +46,13 @@ func TestSendJoinFallback(t *testing.T) {
 		t.Fatalf("failed to marshal RespSendJoin: %s", err)
 	}
 	fc := gomatrixserverlib.NewFederationClient(
-		serverName, keyID, privateKey,
+		[]*gomatrixserverlib.SigningIdentity{
+			{
+				ServerName: serverName,
+				KeyID:      keyID,
+				PrivateKey: privateKey,
+			},
+		},
 		gomatrixserverlib.WithSkipVerify(true),
 	)
 	fc.Client = *gomatrixserverlib.NewClient(gomatrixserverlib.WithTransport(
@@ -76,7 +82,7 @@ func TestSendJoinFallback(t *testing.T) {
 	if err != nil {
 		t.Fatalf("failed to read event json: %s", err)
 	}
-	res, err := fc.SendJoin(context.Background(), targetServerName, ev)
+	res, err := fc.SendJoin(context.Background(), serverName, targetServerName, ev)
 	if err != nil {
 		t.Fatalf("SendJoin returned an error: %s", err)
 	}
@@ -102,7 +108,13 @@ func TestSendJoinJSON(t *testing.T) {
 	}`, string(retEv), string(retEv)))
 
 	fc := gomatrixserverlib.NewFederationClient(
-		serverName, keyID, privateKey,
+		[]*gomatrixserverlib.SigningIdentity{
+			{
+				ServerName: serverName,
+				KeyID:      keyID,
+				PrivateKey: privateKey,
+			},
+		},
 		gomatrixserverlib.WithSkipVerify(true),
 	)
 	fc.Client = *gomatrixserverlib.NewClient(gomatrixserverlib.WithTransport(
@@ -129,7 +141,7 @@ func TestSendJoinJSON(t *testing.T) {
 	if err != nil {
 		t.Fatalf("failed to read event json: %s", err)
 	}
-	res, err := fc.SendJoin(context.Background(), targetServerName, ev)
+	res, err := fc.SendJoin(context.Background(), serverName, targetServerName, ev)
 	if err != nil {
 		t.Fatalf("SendJoin returned an error: %s", err)
 	}
diff --git a/request.go b/request.go
index a1be0008..6d1a2da8 100644
--- a/request.go
+++ b/request.go
@@ -37,8 +37,9 @@ type FederationRequest struct {
 // The destination is the name of a matrix homeserver.
 // The request path must begin with a slash.
 // Eg. NewFederationRequest("GET", "matrix.org", "/_matrix/federation/v1/send/123")
-func NewFederationRequest(method string, destination ServerName, requestURI string) FederationRequest {
+func NewFederationRequest(method string, origin, destination ServerName, requestURI string) FederationRequest {
 	var r FederationRequest
+	r.fields.Origin = origin
 	r.fields.Destination = destination
 	r.fields.Method = strings.ToUpper(method)
 	r.fields.RequestURI = requestURI
diff --git a/request_test.go b/request_test.go
index de0048cf..a18956d5 100644
--- a/request_test.go
+++ b/request_test.go
@@ -47,7 +47,7 @@ const examplePutContent = `{"edus":[{"content":{"device_id":"YHRUBZNPFS",` +
 
 func TestSignGetRequest(t *testing.T) {
 	request := NewFederationRequest(
-		"GET", "localhost:44033",
+		"GET", "localhost:8800", "localhost:44033",
 		"/_matrix/federation/v1/query/directory?room_alias=%23test%3Alocalhost%3A44033",
 	)
 	if err := request.Sign("localhost:8800", "ed25519:a_Obwu", privateKey1); err != nil {
@@ -104,7 +104,7 @@ func TestVerifyGetRequest(t *testing.T) {
 
 func TestSignPutRequest(t *testing.T) {
 	request := NewFederationRequest(
-		"PUT", "localhost:44033", "/_matrix/federation/v1/send/1493385816575/",
+		"PUT", "localhost:8800", "localhost:44033", "/_matrix/federation/v1/send/1493385816575/",
 	)
 	if err := request.SetContent(RawJSON([]byte(examplePutContent))); err != nil {
 		t.Fatal(err)