You can use an IP whitelist in your Node stack to ensure inbound calls originate from only your Apigee services/proxy layer (Apigee proxy is the ‘client’ to your Node stack), but IP whitelisting is usually not considered enough security by today’s standards. Thus, you can also use mTLS (two-way SSL) between Apigee and your Node stack and have your Node stack or its front-end TLS-termination layer validate (from a cert whitelist) the client TLS certificate being presented by Apigee’s proxy layer upon establishing the connection to your back-end.
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