Fix broken token auth when 2FA is enabled

[dekkers]

Changes

Fix broken token auth when 2FA is enabled.

Also add "API" to the "Token authentication" section heading so that the section is return if you search for "API".

Issue link

Closes #2872

QA notes

Enable 2FA and test that the REST API work again.

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Checklist for code reviewers:

Copy-paste the checklist from the docs/source/templates folder into your comment.

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Checklist for QA:

Copy-paste the checklist from the docs/source/templates folder into your comment.

[underdarknl]

Looks good to me.

[ammar92]

Checklist for QA:

• I have checked out this branch, and successfully ran a fresh make reset.
• I confirmed that there are no unintended functional regressions in this branch:
  • I have managed to pass the onboarding flow
  • Objects and Findings are created properly
  • Tasks are created and completed properly
• I confirmed that the PR's advertised feature or hotfix works as intended.
• I checked the logs for errors and/or warnings and made issues where necessary

What works:

• I can access the REST API
  • Works with two-factor enabled
  • Works with two-factor disabled