chore: add source parameter to CustomAuth

[arch1995]

Jira Link

N/A (no ticket in branch name)

Description

This PR adds an optional source parameter to CustomAuth constructor arguments, defaulting to "customauth", and passes it through to the Torus constructor.

Changes:

• CustomAuthArgs: document and add optional source?: string (default "customauth").
• login.ts: destructure source with default and forward it when constructing Torus.

How has this been tested?

• npm run lint:ts — passed
• npm run build — passed
• npm test — all 26 tests passed

Screenshots (if appropriate)

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• My code follows the code style of this project. (run lint)
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

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Note

Low Risk
Low risk: adds a new optional constructor argument with a default and only forwards it to Torus, without changing login flow or data handling.

Overview
Adds an optional source field to CustomAuthArgs (defaulting to "customauth") and wires it through the CustomAuth constructor.

CustomAuth now forwards source into the Torus constructor options, enabling callers to tag the origin of logins without affecting existing integrations.

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