mauerbac/slack-venmo-integration

Venmo integration for Slack. Pay co-workers easily!

Building a Venmo Integration for Slack

Overview

http://bit.ly/slackmo

This is a Venmo Slack integration leveraging Slack’s slash command. Within Slack you can easily pay your co-workers using a simple command. Currently, it supports the ability to pay using their Slack username.

Slash Commands

Slash Commands are a great way to get started with Slack integrations. Anytime a user initiates a slash command (/slackmo), Slack merely POSTs the necessary data to your provided endpoint. A sample request can be seen here:

token=gIkuvaNzQIHg97ATvDxqgjtO
team_id=T0001
team_domain=example
channel_id=C2147483705
channel_name=test
user_id=U2147483697
user_name=Steve
command=/weather
text=94070
response_url=https://hooks.slack.com/commands/1234/5678

You endpoint must parse through this data and provide a JSON response to Slack, so that it can respond back to the user. In this app, we use user_name, user_id & command to make payments on the user’s behalf.

Please Note: This app requires additional consideration around security. Ideally, the user should authenticate with the app every time they attempt to make a payment. A user could spoof one another by making a POST request to my endpoint with another user’s username and pay himself. I think it defeats the purpose of a slash command if a user must authenticate each time, so I’d be curious to see if I’m missing something here.

Usage

Supports 3 commands:

• /slackmo [@username] [$amount] [note] . For example, /slackmo @mauerbac $10 lunch!
• /slackmo help
• /slackmo [@username] add [phone #] - Used for adding a new co-worker

**You can request money by using a negative dollar amount. i.e $-10

Building the app

A first time user will be immediately prompted to Oauth with Venmo. A user must authenticate with Venmo so the app can make payments on their behalf. This token is saved in the app’s database for later use. A Slack username doesn’t necessarily map to a Venmo username, so I needed to create a mapping of Slack username to a Venmo identifying. In this app, I used the Slack username and Venmo phone number. If the receiver hasn’t used the app, you must supply their phone number using the /slackmo @will add [number] command.

The app has two endpoints: /main & /venmoauth, which can be seen in api/views.py. Slack POSTs all slash command data to the main endpoint and Venmo uses the venmoauth endpoint in the OAuth process.

Housekeeping

1. Register a custom slack command.
2. Register an App with Venmo here. Make note of Client ID & Client Secret.
3. Supply Venmo Client ID, Client Secret and Slack Token in api/views.py.
4. Deploy the application and provide Slack with your endpoint.
5. Give it a try!

Next steps

• Add support to refresh Venmo Auth tokens when expired.
• Add better authentication to avoid co-worker spoofing.
• Add additional commands.
• Become an offical Slack Integration via the Slack Button.

Reach out to @mauerbac with questions/feedback. Thanks!