Building an Integrations Marketplace
Maintain your own connectors or use a third party service like Tray.io or Zapier
Tray.io “Embedded" is their white label solution for SaaS platforms. The claims are pretty bold (e.g. can bash out connectors in < 10 days) and the white label/branding is helpful. They have a graphQL api you can use to list available integrations and display them in your app/integrations marketplace page and trigger the OAuth flow for each directly from there. All the OAuth interfaces are under your brand for the end user.