Step Two: Set Up Authorization

Create a connected app in a Salesforce organization and enable OAuth. The client application uses the connected app to connect to Salesforce.

In your Developer Edition organization, from Setup, enter Apps in the Quick Find box, then select Apps, and in the Connected Apps section, click New to create a new connected app.
Clients can use a connected app to sign in to any organization, even if the connected app isn’t defined in that organization.
Enter a connected app name.
Enter the contact email, as well as any other required information.
Select Enable OAuth Settings.
Enter a Callback URL. It must be secure: http:// does not work, only https:// works.
For this quick start, you can simply enter https://.
Enter an OAuth scope. Select Access and manage your Chatter feed in addition to any other scope you want your connected app to allow access to.
Click Save.
The Consumer Key is created and displayed, and a Consumer Secret is created (click the link to reveal it).

Chatter REST API Developer Guide