Deprecating authentication extensions

Octopus Server is phasing out support for custom-built authentication mechanisms by the end of 2023, a decision prompted by the complications and maintenance challenges associated with the existing server extensibility model introduced in Octopus 3.5. Originally implemented to accommodate customer-specific authentication requirements and simplify development, the extensibility model led to unintended complexities and maintenance burdens due to the dependency structures and architectural commitments that became difficult to change over time. While current custom extensions will continue to function with required recompilations for dependency updates, they will cease to work in future builds, prompting Octopus to consolidate customer-created modifications into official providers. Users with entirely custom integrations are encouraged to communicate their needs to Octopus to address potential gaps as the company prioritizes a streamlined, more robust authentication system with enhanced safety checks.