===========

• Setup -> Create -> Apps -> (Connected Apps) New
• Fill Conntected App Name, API Name and Contact Email
• Check the Enable OAuth Settings in the API (Enable OAuth Settings) section
• Callback URL: put a valid URL (you don't need it for the scope of this example)
• Selected OAuth Scopes: select the scopes you want for the NodeJS app acess token to grant
• In the section Canvas App Settings type:
• Canvas App URL: the url of the POST action to be called by Salesforce when injecting the session data (e.g. https://nodejs-canvas-test.herokuapp.com/canvas/callback)
• Access Method: use Signed Request (POST)
• Locations: choose Chatter Tab (the app will be shown in the Chatter page)

Than you need to enable this app

• Setup -> Manage Apps -> Connected Apps -> Your App Name
• In the OAuth policies select Admin approved users are pre-authorized for the Permitted Users field
• In the Profiles related list select your profile (all user of that profile are automatically allowed to consume this app)

There are more ways to configure the Canvas App usage, this is the quicker.

$ heroku config:set SF_CANVASAPP_CLIENT_SECRET=XXXXXXXXX
Adding config vars and restarting myapp... done, v12
SF_CANVASAPP_CLIENT_SECRET: XXXXXXXXX

Go to http://enreeco.blogspot.it/2013/11/salesforce-canvas-nodejs-set-up-minimum.html for a complete description.