Add authenticateSep10 function

[MissBlue00]

Task

Add an authenticateSep10 function for SEP-10 authentication with anchors.

Details

• Function signature: authenticateSep10(config: Sep10Config): Promise<Sep10AuthResult>
• Implement JWT-based authentication flow
• Handle challenge request and response signing
• Return auth token for subsequent anchor calls
• Add Sep10Config and Sep10AuthResult interfaces
• Integration point: anchor-service package

Test

Run pnpm --filter @stellar-pay/anchor-service build to verify no TypeScript errors.

[BigNathan1]

@BigNathan1 has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

I can resolve this issue accurately and precise within the hour. Please assign it to me

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[42natus]

@42natus has applied to work on this issue as part of the Stellar Wave Program's 5th wave.

can i get this please

ℹ️ Repo Maintainers: To accept this application, review their application or assign @42natus to this issue.