Explain how semantic versioning principles apply to API documentation for OTP services when a new, non-breaking authentication endpoint is introduced.

Semantic Versioning, often referred to as SemVer, is a versioning scheme for software that specifies how version numbers are assigned and incremented. It uses a three-part number: MAJOR.MINOR.PATCH. A MAJOR version increment indicates incompatible API changes, meaning existing code may break. A MINOR version increment signifies new, backward-compatible functionality, meaning new features are added without breaking existing ones. A PATCH version increment is for backward-compatible bug fixes. API documentation serves as the authoritative contract for how clients interact with an API, detailing endpoints, request formats, response structures, and authentication methods. OTP services, or One-Time Password services, typically involve APIs for generating, verifying, or validating temporary authentication codes. When a new, non-breaking authentication endpoint is introduced to an API for an OTP service, it means that a new capability is added without altering or removing any existing functionalities or requiring changes to existing client implementations. Because this new endpoint is additive and does not break existing client integrations, it constitutes a new, backward-compatible feature. Therefore, according to Semantic Versioning principles, the API's version number should be incremented at the MINOR level. For example, if the previous API version was 1.0.0, the introduction of this new endpoint would result in the API becoming version 1.1.0. The API documentation must then be updated to reflect this new version. The updated documentation for version 1.1.0 would include the details of the newly introduced authentication endpoint, specifying its purpose, parameters, and responses. Crucially, all the existing endpoints and their specifications from version 1.0.0 would remain fully present and unchanged in the 1.1.0 documentation, demonstrating backward compatibility. Clients that are built against API version 1.0.0 documentation will continue to function correctly, as their expected endpoints and behaviors have not changed. Clients that wish to utilize the newly introduced authentication endpoint would need to refer to the 1.1.0 API documentation to integrate with it. This clear versioning in the documentation ensures that developers understand what capabilities are available at each API version and can confidently upgrade or integrate without unexpected breaking changes.