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Api gateways just grew teeth at the backend. amazon api gateway now presents an acm certificate for…

Yethikrishna ROriginal on Threads

api gateways just grew teeth at the backend. amazon api gateway now presents an acm certificate for mutual tls to your backend integrations, out september 8, so the server that calls you can prove who it is.

the direction of trust in apis just flipped.

Context

AWS's What's New post of September 8, 2026 says you can now configure Amazon API Gateway REST APIs to present an AWS Certificate Manager certificate to your backend during the TLS handshake, enabling mutual TLS, where previously API Gateway could present only a self-signed certificate it generated. It is available in all commercial AWS Regions and GovCloud (US) where REST APIs exist, and is configured through the console, CLI or CloudFormation.

How it compares

The capability is for REST APIs. The current docs say the certificate must be imported into ACM or issued through AWS Private CA, and that ACM public certificates are not supported for backend client authentication, which the docs tie to ACM no longer issuing public certificates with the clientAuth extended key usage as of June 11, 2025. Updates propagate on reimport or renewal without redeployment. These mechanics come from the current docs page, which is undated, and are not a snapshot of the September 8 release. IAM permissions on ACM or ACM PCA are prerequisites. Support for HTTP or WebSocket APIs was not stated.

Watch next

  • The AWS blog's details, and whether other API types are supported.

Sources

  1. AWS: API Gateway mutual TLS to backends (September 8, 2026)aws.amazon.com
  2. AWS docs: ACM client certificates for REST APIsdocs.aws.amazon.com

Provenance

The note above is reproduced unedited from the original post, first published on Threads on 22 September 2026 at 03:18 IST. Sources are the papers and datasets the note draws on.

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