feat: user backend for login and signup

[suzy-g38]

Related Issue

Closes #348

Description

Added login and sign up functionality in the backend

Screenshots

Checklist

• [x] My code adheres to the established style guidelines of the project.
• [x] I have included comments in areas that may be difficult to understand.
• [x] My changes have not introduced any new warnings.
• [x] I have conducted a self-review of my code.

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