Oauth Authentication for FireCloud via API calls

Hi There,

We are integrating our system to fireCloud via APIs(https://api.firecloud.org/). Now to run APIs we need to provide OAuth Token. While testing it via swagger it allows me to log in using EmailID. But, how we need to get this token programmatically? I can see only two APIs under OAuth API list on swagger:
POST /handle-oauth-code
GET /api/refresh-token-status

refresh token looks fine, but how to trigger handle-OAuth-code? what will be redirectUri for this? Looking for urgent help on this.
Note: I'm exploring FISS too but for now we need to integrate using these API calls.