Add token provider infrastructure for token federation (Token Federation 1/3)

[madhav-db]

This PR introduces the foundational token provider system that enables custom token sources for authentication. This is the first of three PRs implementing token federation support.

New components:

• ITokenProvider: Core interface for token providers
• Token: Token class with JWT parsing and expiration handling
• StaticTokenProvider: Provides a constant token
• ExternalTokenProvider: Delegates to a callback function
• TokenProviderAuthenticator: Adapts token providers to IAuthentication

New auth types in ConnectionOptions:

• 'token-provider': Use a custom ITokenProvider
• 'external-token': Use a callback function
• 'static-token': Use a static token string

[Copilot]

Pull request overview

This PR introduces the foundational token provider infrastructure to enable custom token sources for authentication. The implementation adds core interfaces and classes that allow tokens to be sourced from static values, external callbacks, or custom providers, adapting them to work with the existing authentication system.

Key changes:

• Introduces ITokenProvider interface and Token class for token management with JWT parsing and expiration handling
• Adds three concrete provider implementations: StaticTokenProvider, ExternalTokenProvider, and TokenProviderAuthenticator
• Extends connection options with three new auth types: token-provider, external-token, and static-token

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
lib/connection/auth/tokenProvider/ITokenProvider.ts	Defines the core interface for token providers
lib/connection/auth/tokenProvider/Token.ts	Implements token class with JWT parsing, expiration checking, and header management
lib/connection/auth/tokenProvider/StaticTokenProvider.ts	Provides static token implementation with JWT support
lib/connection/auth/tokenProvider/ExternalTokenProvider.ts	Delegates token retrieval to external callback functions
lib/connection/auth/tokenProvider/TokenProviderAuthenticator.ts	Adapts token providers to the IAuthentication interface
lib/connection/auth/tokenProvider/index.ts	Exports public API for token provider components
lib/contracts/IDBSQLClient.ts	Adds new auth types and TokenCallback type definition
lib/DBSQLClient.ts	Implements token provider auth type handling in client
tests/unit/connection/auth/tokenProvider/*.test.ts	Comprehensive test coverage for all token provider components

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