Allow to configure if pushkey should be converted to hex before sendi…

…ng to APNs (#344)

Some APNs libraries give the pushkey in hex directly, but sygnal assumes
that the pushkey is given in base64 (and attempts to convert it to hex).

This adds a configuration option to avoid this processing / assumption.

changelog.d/344.feature

@@ -0,0 +1 @@
+Add a new `convert_device_token_to_hex` configuration option for APNs apps, to allow disabling the conversion of device tokens from base64 to hex.

sygnal.yaml.sample

@@ -197,6 +197,11 @@ apps:
   #  #
   #  # The default is 'production'. Uncomment to use the sandbox instance.
   #  #platform: sandbox
+  #  #
+  #  # Specifies whether to convert the device push token from base 64 to hex.
+  #  # Defaults to True, set this to False if your client library provides a
+  #  # push token in hex format.
+  #  #convert_device_token_to_hex: false
 
   # This is an example GCM/FCM push configuration.
   #

sygnal/apnspushkin.py

@@ -238,7 +238,12 @@ async def _dispatch_request(
         """
         span.set_tag("apns_id", notif_id)
 
-        device_token = base64.b64decode(device.pushkey).hex()
+        # Some client libraries will provide the push token in hex format already. Avoid
+        # attempting to convert from base 64 to hex.
+        if self.get_config("convert_device_token_to_hex", bool, True):
+            device_token = base64.b64decode(device.pushkey).hex()
+        else:
+            device_token = device.pushkey
 
         request = NotificationRequest(
             device_token=device_token,