added discord oauth and callback

[boyuan12]

Description

Please include a summary of the change and which issue is fixed. Added Discord OAuth and callback. Access token are stored in the user's session. Discord client ID and secret are stored in environment variables. All field needed for the User model are stored in appropriate variables: email, username, discriminator (the 4-digit number after the Discord username), discord_id, in_fellowship (boolean, True if user is in fellowship server, false otherwise.)

Please also include relevant motivation and context. Discord OAuth

List any dependencies that are required for this change. requests

Fixes # (issue) fixed #11

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] Any dependent changes have been merged and published in downstream modules

Screenshots

N/A

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