Add Whatsapp message support for Twilio outbound connector

[jan-ladleif]

Is your feature request related to a problem? Please describe.

I want to set up inbound and outbound connectors for Whatsapp messaging via Twilio. There is already an out-of-the-box Twilio connector.

Describe the solution you'd like

The Twilio inbound connector seems to pick up the Whatsapp webhook calls by Twilio fine.

However, the outbound connector currently only offers Camunda users to send SMS messages. The same Twilio API can be used for Whatsapp messages, but different headers are required. These can be configured using element templates, but the required fields do not come with the standard connector.

The outbound connector element template should be extended with an operation type "Send Whatsapp message" that then offers users to input the required header variables.

Describe alternatives you've considered

We considered using a native Whatsapp business connector, but...

• There is only an outbound one, not inbound.
• Getting a Whatsapp business account is apparently difficult, so Twilio is preferred.

Additional context

No further context

[jan-ladleif]

cc @vobu @camundom

[jan-ladleif]

After some more research, the scope boils down to two aspects:

• The existing Twilio connector does already work for both SMS and Whatsapp messages (inbound and outbound), but the latter need a whatsapp: prefix in front of the phone numbers. This should be clarified in the documentation, and could also be mentioned in the Element Template.
• An extension is necessary to make use of Whatsapp templates in the outbound case to fill in the template ID and the replacement variables. Will work together with @camundom on this in the Element Template based on his previous work.

[jan-ladleif]

I am encountering a bit of a roadblock: One of the ways to send Whatsapp messages is to use templates (required for initial contact). A template is a text with numbered placeholders, e.g.,

Your appointment is coming up on {{1}} at {{2}}.
If you need to change it, please reply back and let us know.

In the request to Twilio's Messaging endpoint you have to provide replacement values as an escaped JSON string. To add this to the element template, I see two options (other than a static value):

Option 1 (fallback): User needs to provide escaped JSON string

Quite error-prone and does not look great, but together with FEEL string concatenation you could also include scope variables. This works.

Option 2 (preferred): User provides a FEEL context

Would feel very native and integrated, easy to combine with other FEEL structures. However, this fails with an error: "The ContentVariables Parameter is invalid"

I suspect this is due to our HTTP request treating the FEEL context as a JSON object and sending it as a JSON object as well, rather than an escaped JSON string. Some custom logging output supports this (compare the ContentVariables in the body):

-- Option 1
POST https://api.twilio.com/2010-04-01/Accounts/xxx/Messages.json body:
{
"ContentSid":"xxx",
"ContentVariables":"{\"1\":\"Tuesday\", \"2\":\"2pm\"}",
"From":"whatsapp:+xxx","To":"whatsapp:+xxx"
}

-- Option 2
POST https://api.twilio.com/2010-04-01/Accounts/xxx/Messages.json body:
{
"ContentSid":"xxx",
"ContentVariables":{"1":"xyz","2":"foo"},
"From":"whatsapp:+xxx","To":"whatsapp:+xxx"
}

(tbc in a few hours)