refactor: use HTTP constants in code

Description

Use http constants in the code instead of hard-coded values

Related Issues

Resolves #1267 (closed)

How has this been tested?

I mostly rely on tests (where it's covered) and careful double-check of replaced values with proper constants.

Screenshots (if appropriate):

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 change)
• Documentation
• Chore (Related to CI or Packaging to platforms)
• Test gap
• Refactoring

Closes #1267 (closed)