diff --git a/package.json b/package.json
index 341ab850b..02a5c4cee 100644
--- a/package.json
+++ b/package.json
@@ -55,7 +55,7 @@
     ],
     "dependencies": {
         "@babel/runtime": "^7.12.5",
-        "@matrix-org/matrix-sdk-crypto-js": "^0.1.0-alpha.8",
+        "@matrix-org/matrix-sdk-crypto-js": "^0.1.0-alpha.9",
         "another-json": "^0.2.0",
         "bs58": "^5.0.0",
         "content-type": "^1.0.4",
diff --git a/spec/unit/rust-crypto/OutgoingRequestProcessor.spec.ts b/spec/unit/rust-crypto/OutgoingRequestProcessor.spec.ts
index 28d1e9b35..bb1cdff6a 100644
--- a/spec/unit/rust-crypto/OutgoingRequestProcessor.spec.ts
+++ b/spec/unit/rust-crypto/OutgoingRequestProcessor.spec.ts
@@ -24,11 +24,12 @@ import {
     KeysUploadRequest,
     RoomMessageRequest,
     SignatureUploadRequest,
+    SigningKeysUploadRequest,
     ToDeviceRequest,
 } from "@matrix-org/matrix-sdk-crypto-js";
 
 import { TypedEventEmitter } from "../../../src/models/typed-event-emitter";
-import { HttpApiEvent, HttpApiEventHandlerMap, MatrixHttpApi } from "../../../src";
+import { HttpApiEvent, HttpApiEventHandlerMap, MatrixHttpApi, UIAuthCallback } from "../../../src";
 import { OutgoingRequestProcessor } from "../../../src/rust-crypto/OutgoingRequestProcessor";
 
 describe("OutgoingRequestProcessor", () => {
@@ -80,6 +81,12 @@ describe("OutgoingRequestProcessor", () => {
             "https://example.com/_matrix/client/v3/keys/signatures/upload",
         ],
         ["KeysBackupRequest", KeysBackupRequest, "PUT", "https://example.com/_matrix/client/v3/room_keys/keys"],
+        [
+            "SigningKeysUploadRequest",
+            SigningKeysUploadRequest,
+            "POST",
+            "https://example.com/_matrix/client/v3/keys/device_signing/upload",
+        ],
     ];
 
     test.each(tests)(`should handle %ss`, async (_, RequestClass, expectedMethod, expectedPath) => {
@@ -171,6 +178,40 @@ describe("OutgoingRequestProcessor", () => {
         httpBackend.verifyNoOutstandingRequests();
     });
 
+    it("should handle SigningKeysUploadRequests with UIA", async () => {
+        // first, mock up a request as we might expect to receive it from the Rust layer ...
+        const testReq = { foo: "bar" };
+        const outgoingRequest = new SigningKeysUploadRequest("1234", JSON.stringify(testReq));
+
+        // also create a UIA callback
+        const authCallback: UIAuthCallback<Object> = async (makeRequest) => {
+            return await makeRequest({ type: "test" });
+        };
+
+        // ... then poke the request into the OutgoingRequestProcessor under test
+        const reqProm = processor.makeOutgoingRequest(outgoingRequest, authCallback);
+
+        // Now: check that it makes a matching HTTP request ...
+        const testResponse = '{"result":1}';
+        httpBackend
+            .when("POST", "/_matrix")
+            .check((req) => {
+                expect(req.path).toEqual("https://example.com/_matrix/client/v3/keys/device_signing/upload");
+                expect(JSON.parse(req.rawData)).toEqual({ foo: "bar", auth: { type: "test" } });
+                expect(req.headers["Accept"]).toEqual("application/json");
+                expect(req.headers["Content-Type"]).toEqual("application/json");
+            })
+            .respond(200, testResponse, true);
+
+        // ... and that it calls OlmMachine.markAsSent.
+        const markSentCallPromise = awaitCallToMarkAsSent();
+        await httpBackend.flushAllExpected();
+
+        await Promise.all([reqProm, markSentCallPromise]);
+        expect(olmMachine.markRequestAsSent).toHaveBeenCalledWith("1234", outgoingRequest.type, testResponse);
+        httpBackend.verifyNoOutstandingRequests();
+    });
+
     it("does not explode with unknown requests", async () => {
         const outgoingRequest = { id: "5678", type: 987 };
         const markSentCallPromise = awaitCallToMarkAsSent();
diff --git a/src/rust-crypto/OutgoingRequestProcessor.ts b/src/rust-crypto/OutgoingRequestProcessor.ts
index 7ac9a2105..4e98bce8d 100644
--- a/src/rust-crypto/OutgoingRequestProcessor.ts
+++ b/src/rust-crypto/OutgoingRequestProcessor.ts
@@ -23,11 +23,14 @@ import {
     RoomMessageRequest,
     SignatureUploadRequest,
     ToDeviceRequest,
+    SigningKeysUploadRequest,
 } from "@matrix-org/matrix-sdk-crypto-js";
 
 import { logger } from "../logger";
 import { IHttpOpts, MatrixHttpApi, Method } from "../http-api";
 import { QueryDict } from "../utils";
+import { IAuthDict, UIAuthCallback } from "../interactive-auth";
+import { UIAResponse } from "../@types/uia";
 
 /**
  * Common interface for all the request types returned by `OlmMachine.outgoingRequests`.
@@ -53,7 +56,7 @@ export class OutgoingRequestProcessor {
         private readonly http: MatrixHttpApi<IHttpOpts & { onlyData: true }>,
     ) {}
 
-    public async makeOutgoingRequest(msg: OutgoingRequest): Promise<void> {
+    public async makeOutgoingRequest<T>(msg: OutgoingRequest, uiaCallback?: UIAuthCallback<T>): Promise<void> {
         let resp: string;
 
         /* refer https://docs.rs/matrix-sdk-crypto/0.6.0/matrix_sdk_crypto/requests/enum.OutgoingRequests.html
@@ -79,6 +82,14 @@ export class OutgoingRequestProcessor {
                 `/_matrix/client/v3/room/${encodeURIComponent(msg.room_id)}/send/` +
                 `${encodeURIComponent(msg.event_type)}/${encodeURIComponent(msg.txn_id)}`;
             resp = await this.rawJsonRequest(Method.Put, path, {}, msg.body);
+        } else if (msg instanceof SigningKeysUploadRequest) {
+            resp = await this.makeRequestWithUIA(
+                Method.Post,
+                "/_matrix/client/v3/keys/device_signing/upload",
+                {},
+                msg.body,
+                uiaCallback,
+            );
         } else {
             logger.warn("Unsupported outgoing message", Object.getPrototypeOf(msg));
             resp = "";
@@ -89,6 +100,31 @@ export class OutgoingRequestProcessor {
         }
     }
 
+    private async makeRequestWithUIA<T>(
+        method: Method,
+        path: string,
+        queryParams: QueryDict,
+        body: string,
+        uiaCallback: UIAuthCallback<T> | undefined,
+    ): Promise<string> {
+        if (!uiaCallback) {
+            return await this.rawJsonRequest(method, path, queryParams, body);
+        }
+
+        const parsedBody = JSON.parse(body);
+        const makeRequest = async (auth: IAuthDict): Promise<UIAResponse<T>> => {
+            const newBody = {
+                ...parsedBody,
+                auth,
+            };
+            const resp = await this.rawJsonRequest(method, path, queryParams, JSON.stringify(newBody));
+            return JSON.parse(resp) as T;
+        };
+
+        const resp = await uiaCallback(makeRequest);
+        return JSON.stringify(resp);
+    }
+
     private async rawJsonRequest(method: Method, path: string, queryParams: QueryDict, body: string): Promise<string> {
         const opts = {
             // inhibit the JSON stringification and parsing within HttpApi.
diff --git a/yarn.lock b/yarn.lock
index 07a9e8e70..7f0917823 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1426,10 +1426,10 @@
   dependencies:
     lodash "^4.17.21"
 
-"@matrix-org/matrix-sdk-crypto-js@^0.1.0-alpha.8":
-  version "0.1.0-alpha.8"
-  resolved "https://registry.yarnpkg.com/@matrix-org/matrix-sdk-crypto-js/-/matrix-sdk-crypto-js-0.1.0-alpha.8.tgz#18dd8e7fb56602d2999d8a502b49e902a2bb3782"
-  integrity sha512-hdmbbGXKrN6JNo3wdBaR5Zs3lXlzllT3U43ViNTlabB3nKkOZQnEAN/Isv+4EQSgz1+8897veI9Q8sqlQX22oA==
+"@matrix-org/matrix-sdk-crypto-js@^0.1.0-alpha.9":
+  version "0.1.0-alpha.9"
+  resolved "https://registry.yarnpkg.com/@matrix-org/matrix-sdk-crypto-js/-/matrix-sdk-crypto-js-0.1.0-alpha.9.tgz#00bc266781502641a661858a5a521dd4d95275fc"
+  integrity sha512-g5cjpFwA9h0CbEGoAqNVI2QcyDsbI8FHoLo9+OXWHIezEKITsSv78mc5ilIwN+2YpmVlH0KNeQWTHw4vi0BMnw==
 
 "@matrix-org/olm@https://gitlab.matrix.org/api/v4/projects/27/packages/npm/@matrix-org/olm/-/@matrix-org/olm-3.2.14.tgz":
   version "3.2.14"