diff --git a/appservice/intent.go b/appservice/intent.go
index 0ec10b77..5d43f190 100644
--- a/appservice/intent.go
+++ b/appservice/intent.go
@@ -51,7 +51,7 @@ func (as *AppService) NewIntentAPI(localpart string) *IntentAPI {
 }
 
 func (intent *IntentAPI) Register(ctx context.Context) error {
-	_, err := intent.Client.MakeRequest(ctx, http.MethodPost, intent.BuildClientURL("v3", "register"), &mautrix.ReqRegister{
+	_, err := intent.Client.MakeRequest(ctx, http.MethodPost, intent.BuildClientURL("v3", "register"), &mautrix.ReqRegister[any]{
 		Username:     intent.Localpart,
 		Type:         mautrix.AuthTypeAppservice,
 		InhibitLogin: true,
diff --git a/client.go b/client.go
index fbb9333f..7062d9b9 100644
--- a/client.go
+++ b/client.go
@@ -918,7 +918,7 @@ func (cli *Client) RegisterAvailable(ctx context.Context, username string) (resp
 	return
 }
 
-func (cli *Client) register(ctx context.Context, url string, req *ReqRegister) (resp *RespRegister, uiaResp *RespUserInteractive, err error) {
+func (cli *Client) register(ctx context.Context, url string, req *ReqRegister[any]) (resp *RespRegister, uiaResp *RespUserInteractive, err error) {
 	var bodyBytes []byte
 	bodyBytes, err = cli.MakeFullRequest(ctx, FullRequest{
 		Method:           http.MethodPost,
@@ -942,7 +942,7 @@ func (cli *Client) register(ctx context.Context, url string, req *ReqRegister) (
 // Register makes an HTTP request according to https://spec.matrix.org/v1.2/client-server-api/#post_matrixclientv3register
 //
 // Registers with kind=user. For kind=guest, see RegisterGuest.
-func (cli *Client) Register(ctx context.Context, req *ReqRegister) (*RespRegister, *RespUserInteractive, error) {
+func (cli *Client) Register(ctx context.Context, req *ReqRegister[any]) (*RespRegister, *RespUserInteractive, error) {
 	u := cli.BuildClientURL("v3", "register")
 	return cli.register(ctx, u, req)
 }
@@ -951,7 +951,7 @@ func (cli *Client) Register(ctx context.Context, req *ReqRegister) (*RespRegiste
 // with kind=guest.
 //
 // For kind=user, see Register.
-func (cli *Client) RegisterGuest(ctx context.Context, req *ReqRegister) (*RespRegister, *RespUserInteractive, error) {
+func (cli *Client) RegisterGuest(ctx context.Context, req *ReqRegister[any]) (*RespRegister, *RespUserInteractive, error) {
 	query := map[string]string{
 		"kind": "guest",
 	}
@@ -974,7 +974,7 @@ func (cli *Client) RegisterGuest(ctx context.Context, req *ReqRegister) (*RespRe
 //		panic(err)
 //	}
 //	token := res.AccessToken
-func (cli *Client) RegisterDummy(ctx context.Context, req *ReqRegister) (*RespRegister, error) {
+func (cli *Client) RegisterDummy(ctx context.Context, req *ReqRegister[any]) (*RespRegister, error) {
 	_, uia, err := cli.Register(ctx, req)
 	if err != nil && uia == nil {
 		return nil, err
@@ -2687,13 +2687,13 @@ func (cli *Client) SetDeviceInfo(ctx context.Context, deviceID id.DeviceID, req
 	return err
 }
 
-func (cli *Client) DeleteDevice(ctx context.Context, deviceID id.DeviceID, req *ReqDeleteDevice) error {
+func (cli *Client) DeleteDevice(ctx context.Context, deviceID id.DeviceID, req *ReqDeleteDevice[any]) error {
 	urlPath := cli.BuildClientURL("v3", "devices", deviceID)
 	_, err := cli.MakeRequest(ctx, http.MethodDelete, urlPath, req, nil)
 	return err
 }
 
-func (cli *Client) DeleteDevices(ctx context.Context, req *ReqDeleteDevices) error {
+func (cli *Client) DeleteDevices(ctx context.Context, req *ReqDeleteDevices[any]) error {
 	urlPath := cli.BuildClientURL("v3", "delete_devices")
 	_, err := cli.MakeRequest(ctx, http.MethodPost, urlPath, req, nil)
 	return err
@@ -2704,7 +2704,7 @@ type UIACallback = func(*RespUserInteractive) interface{}
 // UploadCrossSigningKeys uploads the given cross-signing keys to the server.
 // Because the endpoint requires user-interactive authentication a callback must be provided that,
 // given the UI auth parameters, produces the required result (or nil to end the flow).
-func (cli *Client) UploadCrossSigningKeys(ctx context.Context, keys *UploadCrossSigningKeysReq, uiaCallback UIACallback) error {
+func (cli *Client) UploadCrossSigningKeys(ctx context.Context, keys *UploadCrossSigningKeysReq[any], uiaCallback UIACallback) error {
 	content, err := cli.MakeFullRequest(ctx, FullRequest{
 		Method:           http.MethodPost,
 		URL:              cli.BuildClientURL("v3", "keys", "device_signing", "upload"),
diff --git a/crypto/cross_sign_key.go b/crypto/cross_sign_key.go
index 4094f695..5d9bf5b3 100644
--- a/crypto/cross_sign_key.go
+++ b/crypto/cross_sign_key.go
@@ -135,7 +135,7 @@ func (mach *OlmMachine) PublishCrossSigningKeys(ctx context.Context, keys *Cross
 	}
 	userKey.Signatures = signatures.NewSingleSignature(userID, id.KeyAlgorithmEd25519, keys.MasterKey.PublicKey().String(), userSig)
 
-	err = mach.Client.UploadCrossSigningKeys(ctx, &mautrix.UploadCrossSigningKeysReq{
+	err = mach.Client.UploadCrossSigningKeys(ctx, &mautrix.UploadCrossSigningKeysReq[any]{
 		Master:      masterKey,
 		SelfSigning: selfKey,
 		UserSigning: userKey,
diff --git a/mockserver/mockserver.go b/mockserver/mockserver.go
index e52c387a..507c24a5 100644
--- a/mockserver/mockserver.go
+++ b/mockserver/mockserver.go
@@ -231,7 +231,7 @@ func (ms *MockServer) postKeysUpload(w http.ResponseWriter, r *http.Request) {
 }
 
 func (ms *MockServer) postDeviceSigningUpload(w http.ResponseWriter, r *http.Request) {
-	var req mautrix.UploadCrossSigningKeysReq
+	var req mautrix.UploadCrossSigningKeysReq[any]
 	mustDecode(r, &req)
 
 	userID := ms.getUserID(r).UserID
diff --git a/requests.go b/requests.go
index 397d30de..cc8b7266 100644
--- a/requests.go
+++ b/requests.go
@@ -66,14 +66,14 @@ const (
 )
 
 // ReqRegister is the JSON request for https://spec.matrix.org/v1.2/client-server-api/#post_matrixclientv3register
-type ReqRegister struct {
+type ReqRegister[UIAType any] struct {
 	Username                 string      `json:"username,omitempty"`
 	Password                 string      `json:"password,omitempty"`
 	DeviceID                 id.DeviceID `json:"device_id,omitempty"`
 	InitialDeviceDisplayName string      `json:"initial_device_display_name,omitempty"`
 	InhibitLogin             bool        `json:"inhibit_login,omitempty"`
 	RefreshToken             bool        `json:"refresh_token,omitempty"`
-	Auth                     interface{} `json:"auth,omitempty"`
+	Auth                     UIAType     `json:"auth,omitempty"`
 
 	// Type for registration, only used for appservice user registrations
 	// https://spec.matrix.org/v1.2/application-service-api/#server-admin-style-permissions
@@ -320,11 +320,11 @@ func (csk *CrossSigningKeys) FirstKey() id.Ed25519 {
 	return ""
 }
 
-type UploadCrossSigningKeysReq struct {
+type UploadCrossSigningKeysReq[UIAType any] struct {
 	Master      CrossSigningKeys `json:"master_key"`
 	SelfSigning CrossSigningKeys `json:"self_signing_key"`
 	UserSigning CrossSigningKeys `json:"user_signing_key"`
-	Auth        interface{}      `json:"auth,omitempty"`
+	Auth        UIAType          `json:"auth,omitempty"`
 }
 
 type KeyMap map[id.DeviceKeyID]string
@@ -392,14 +392,14 @@ type ReqDeviceInfo struct {
 }
 
 // ReqDeleteDevice is the JSON request for https://spec.matrix.org/v1.2/client-server-api/#delete_matrixclientv3devicesdeviceid
-type ReqDeleteDevice struct {
-	Auth interface{} `json:"auth,omitempty"`
+type ReqDeleteDevice[UIAType any] struct {
+	Auth UIAType `json:"auth,omitempty"`
 }
 
 // ReqDeleteDevices is the JSON request for https://spec.matrix.org/v1.2/client-server-api/#post_matrixclientv3delete_devices
-type ReqDeleteDevices struct {
+type ReqDeleteDevices[UIAType any] struct {
 	Devices []id.DeviceID `json:"devices"`
-	Auth    interface{}   `json:"auth,omitempty"`
+	Auth    UIAType       `json:"auth,omitempty"`
 }
 
 type ReqPutPushRule struct {