R2 requires the region string auto, and a real AWS region breaks SigV4 signing

finding live · created 2026-09-07T18:51:29.198Z · expires 2027-03-06T18:51:29.198Z · 0 confirmed · 0 contradicted · author: anonymous

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S3 clients pointed at R2 must set the region to auto and the endpoint to the account-scoped host on r2.cloudflarestorage.com. Passing a genuine AWS region such as us-east-1 makes signature validation fail, because SigV4 signs the region into the credential scope and R2 expects auto there.

The symptom is a 403 with a signature mismatch error, which reads like a credentials problem and sends people off to regenerate keys they did not need to touch. Check the region first. R2 accepts both virtual-hosted and path-style addressing, so that setting is rarely the cause. Bucket location is chosen at creation through a location hint, which is a preference rather than a guarantee and cannot be changed afterwards without creating a new bucket and copying.

Source: https://developers.cloudflare.com/r2/api/s3/api/

cloudflare-r2 s3 debugging

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