diff --git a/ghost/ghost/src/core/activitypub/http-signature.service.test.ts b/ghost/ghost/src/core/activitypub/http-signature.service.test.ts
index c327196623..0b969cb0cc 100644
--- a/ghost/ghost/src/core/activitypub/http-signature.service.test.ts
+++ b/ghost/ghost/src/core/activitypub/http-signature.service.test.ts
@@ -1,4 +1,5 @@
 import assert from 'assert';
+import crypto from 'crypto';
 import {HTTPSignature} from './http-signature.service';
 
 describe('HTTPSignature', function () {
@@ -50,4 +51,50 @@ describe('HTTPSignature', function () {
             assert.equal(actual, expected, 'The signature should have been validated');
         });
     });
+
+    describe('#sign', function () {
+        it('Can sign a request that does not have explicit Date or Host headers', async function () {
+            const keypair = crypto.generateKeyPairSync('rsa', {
+                modulusLength: 512
+            });
+            const request = new Request('https://example.com:2368/blah');
+            const signed = await HTTPSignature.sign(request, new URL('https://keyid.com'), keypair.privateKey);
+
+            assert.ok(signed);
+        });
+
+        it('Can sign a post request which is valid', async function () {
+            const keypair = crypto.generateKeyPairSync('rsa', {
+                modulusLength: 512
+            });
+            class MockHTTPSignature extends HTTPSignature {
+                protected static async getPublicKey() {
+                    return keypair.publicKey;
+                }
+            }
+
+            const request = new Request('https://example.com:2368/blah', {
+                method: 'POST',
+                headers: {
+                    'Content-Type': 'application/ld+json'
+                },
+                body: JSON.stringify({
+                    id: 'https://mastodon.social/users/testingshtuff',
+                    type: 'Accept',
+                    actor: 'https://mastodon.social/users/testingshtuff',
+                    object: 'https://mastodon.social/79f89120-fd13-43e8-aa6d-3bd03652cfad'
+                })
+            });
+
+            const signed = await MockHTTPSignature.sign(request, new URL('https://keyid.com'), keypair.privateKey);
+
+            assert.ok(signed);
+
+            const url = new URL(signed.url);
+            const body = Buffer.from(await signed.text());
+            const result = await MockHTTPSignature.validate(signed.method, url.pathname, signed.headers, body);
+
+            assert.equal(result, true);
+        });
+    });
 });
diff --git a/ghost/ghost/src/core/activitypub/http-signature.service.ts b/ghost/ghost/src/core/activitypub/http-signature.service.ts
index ba9824dc83..48920e2918 100644
--- a/ghost/ghost/src/core/activitypub/http-signature.service.ts
+++ b/ghost/ghost/src/core/activitypub/http-signature.service.ts
@@ -106,7 +106,9 @@ export class HTTPSignature {
             .update(requestBody)
             .digest('base64');
 
-        const remoteDigest = requestHeaders.get('digest')?.split('SHA-256=')[1];
+        const parts = requestHeaders.get('digest')?.split('=');
+        parts?.shift();
+        const remoteDigest = parts?.join('=');
 
         return digest === remoteDigest;
     }
@@ -168,9 +170,24 @@ export class HTTPSignature {
             algorithm: 'rsa-sha256'
         };
         const url = new URL(request.url);
+        const requestHeaders = new Headers(request.headers);
+        if (!requestHeaders.has('host')) {
+            requestHeaders.set('host', url.host);
+        }
+        if (!requestHeaders.has('date')) {
+            requestHeaders.set('date', (new Date()).toUTCString());
+        }
+        if (request.method.toLowerCase() === 'post') {
+            const digest = crypto
+                .createHash(signatureData.algorithm)
+                .update(Buffer.from(await request.clone().text(), 'utf8'))
+                .digest('base64');
+
+            requestHeaders.set('digest', `${signatureData.algorithm}=${digest}`);
+        }
         const signatureString = this.generateSignatureString(
             signatureData,
-            request.headers,
+            requestHeaders,
             request.method,
             url.pathname
         );
@@ -180,14 +197,13 @@ export class HTTPSignature {
             .sign(privateKey)
             .toString('base64');
 
-        const newHeaders = new Headers(request.headers);
-        newHeaders.set(
+        requestHeaders.set(
             'Signature',
             `keyId="${keyId}",headers="${headers.join(' ')}",signature="${signature}",algorithm="${signatureData.algorithm}"`
         );
 
         return new Request(request, {
-            headers: newHeaders
+            headers: requestHeaders
         });
     }
 }