diff --git a/changelog.d/4408.misc b/changelog.d/4408.misc
new file mode 100644
index 000000000..729bafd62
--- /dev/null
+++ b/changelog.d/4408.misc
@@ -0,0 +1 @@
+Refactor 'sign_request' as 'build_auth_headers'
\ No newline at end of file
diff --git a/synapse/handlers/identity.py b/synapse/handlers/identity.py
index 5feb3f22a..39184f0e2 100644
--- a/synapse/handlers/identity.py
+++ b/synapse/handlers/identity.py
@@ -167,18 +167,21 @@ class IdentityHandler(BaseHandler):
             "mxid": mxid,
             "threepid": threepid,
         }
-        headers = {}
+
         # we abuse the federation http client to sign the request, but we have to send it
         # using the normal http client since we don't want the SRV lookup and want normal
         # 'browser-like' HTTPS.
-        self.federation_http_client.sign_request(
+        auth_headers = self.federation_http_client.build_auth_headers(
             destination=None,
             method='POST',
             url_bytes='/_matrix/identity/api/v1/3pid/unbind'.encode('ascii'),
-            headers_dict=headers,
             content=content,
             destination_is=id_server,
         )
+        headers = {
+            b"Authorization": auth_headers,
+        }
+
         try:
             yield self.http_client.post_json_get_json(
                 url,
diff --git a/synapse/http/matrixfederationclient.py b/synapse/http/matrixfederationclient.py
index f2a42f97a..ea2fc64b9 100644
--- a/synapse/http/matrixfederationclient.py
+++ b/synapse/http/matrixfederationclient.py
@@ -298,9 +298,9 @@ class MatrixFederationHttpClient(object):
                     json = request.get_json()
                     if json:
                         headers_dict[b"Content-Type"] = [b"application/json"]
-                        self.sign_request(
+                        auth_headers = self.build_auth_headers(
                             destination_bytes, method_bytes, url_to_sign_bytes,
-                            headers_dict, json,
+                            json,
                         )
                         data = encode_canonical_json(json)
                         producer = FileBodyProducer(
@@ -309,11 +309,12 @@ class MatrixFederationHttpClient(object):
                         )
                     else:
                         producer = None
-                        self.sign_request(
+                        auth_headers = self.build_auth_headers(
                             destination_bytes, method_bytes, url_to_sign_bytes,
-                            headers_dict,
                         )
 
+                    headers_dict[b"Authorization"] = auth_headers
+
                     logger.info(
                         "{%s} [%s] Sending request: %s %s",
                         request.txn_id, request.destination, request.method,
@@ -440,24 +441,23 @@ class MatrixFederationHttpClient(object):
 
             defer.returnValue(response)
 
-    def sign_request(self, destination, method, url_bytes, headers_dict,
-                     content=None, destination_is=None):
+    def build_auth_headers(
+        self, destination, method, url_bytes, content=None, destination_is=None,
+    ):
         """
-        Signs a request by adding an Authorization header to headers_dict
+        Builds the Authorization headers for a federation request
         Args:
             destination (bytes|None): The desination home server of the request.
                 May be None if the destination is an identity server, in which case
                 destination_is must be non-None.
             method (bytes): The HTTP method of the request
             url_bytes (bytes): The URI path of the request
-            headers_dict (dict[bytes, list[bytes]]): Dictionary of request headers to
-                append to
             content (object): The body of the request
             destination_is (bytes): As 'destination', but if the destination is an
                 identity server
 
         Returns:
-            None
+            list[bytes]: a list of headers to be added as "Authorization:" headers
         """
         request = {
             "method": method,
@@ -484,8 +484,7 @@ class MatrixFederationHttpClient(object):
                     self.server_name, key, sig,
                 )).encode('ascii')
             )
-
-        headers_dict[b"Authorization"] = auth_headers
+        return auth_headers
 
     @defer.inlineCallbacks
     def put_json(self, destination, path, args={}, data={},