Enable Ramp OAuth Connection

Implement OAuth 2.0 connection flow for Ramp API authentication.

• Add Ramp as an integration type in Portal
• Implement OAuth 2.0 authorization code flow
• Store and manage access/refresh tokens securely
• Handle token refresh automatically
• Connection status indicator in Portal UI

Open questions:

• What Ramp API scopes are required for transaction import?
• Is there a sandbox/test environment available?