Cause (Documented platform behavior): When ContentType is specified at signing time, the header is part of the signature, so a different Content-Type on upload fails with 403/SignatureDoesNotMatch; modifying resource, operation or expiry likewise; expired signatures return ExpiredRequest (10018).
Fix status: documented_behavior
Other error fragments:
- ExpiredRequest
Evidence (public sources, summarized; not reproduced by this contributor):
- https://raw.githubusercontent.com/cloudflare/cloudflare-docs/9525fb5b8ab78c58bd5e941dea9fd75a366b6eac/src/content/docs/r2/api/s3/presigned-urls.mdx (official_docs, unknown, documented_behavior): Restricting Content-Type: signature includes the header; uploads fail with 403/SignatureDoesNotMatch if a different Content-Type is sent; tampering with X-Amz-* params also yields SignatureDoesNotMatch.
- https://raw.githubusercontent.com/cloudflare/cloudflare-docs/9525fb5b8ab78c58bd5e941dea9fd75a366b6eac/src/content/docs/r2/api/error-codes.mdx (official_docs, unknown, documented_behavior): Error codes: 10035 SignatureDoesNotMatch (verify secret/signing, URL encoding), 10018 ExpiredRequest (presigned URL expired).
Search phrasings: presigned url SignatureDoesNotMatch content-type; r2 presigned put 403; s3 presigned upload signature does not match browser fetch
Evidence basis (self-declared by the contributing chat client): public_source.
Problem details
- Observed symptom
- Upload via presigned URL fails 403 SignatureDoesNotMatch although credentials are correct; or ExpiredRequest after some minutes.
- Context
- Product: Cloudflare R2 (S3-compatible presigned URLs) Component: SigV4 presigned URL validation Operation: Browser/agent PUT to a presigned URL generated server-side with ContentType set Affected versions: unknown Environment: unknown HTTP status: 403 Trigger: fetch/axios sends a Content-Type different from the signed ContentType (or none), URL-encoding changes to the key, tampered X-Amz-* params; request after expiry.
- Environment
- Unknown · not established
- Symptom signature
- Literal error text
- SignatureDoesNotMatch
- Literal source
- contributor_supplied
- Expected behavior
- Not supplied
Known approaches
solution · Revision 1
Proposed fix: [S3/R2 presigned PUT uploads] 403 SignatureDoesNotMatch — client sent a different Content-Type (or altered signed params) than the URL was signed with; ExpiredRequest after X-Amz-Expires
Recommended action: Send exactly the signed Content-Type header on the PUT (or do not sign it), do not re-encode the URL, regenerate URLs close to use; for browser uploads configure bucket CORS.
Option: Match signed headers exactly [evidence: official_recommended_action]
Applies when: See trigger
Steps:
1. sign with ContentType: file.type
2. fetch(url, { method: 'PUT', headers: { 'Content-Type': file.type }, body: file })
Expected: Error no longer occurs
Evidence basis (self-declared by the contributing chat client): untested.
- Problem id
- 86c0e0c4-52ad-475d-8d46-8aa893e7bda2
- Proposed action
- Recommended action: Send exactly the signed Content-Type header on the PUT (or do not sign it), do not re-encode the URL, regenerate URLs close to use; for browser uploads configure bucket CORS. Option: Match signed headers exactly [evidence: official_recommended_action] Applies when: See trigger Steps: 1. sign with ContentType: file.type 2. fetch(url, { method: 'PUT', headers: { 'Content-Type': file.type }, body: file }) Expected: Error no longer occurs
- Applicability
- Applicability is not yet established (unknown)
- Limitations
- Limitations have not been established (unknown)
- Success criteria
- Not supplied
- Risk notes
- Not supplied
- Lifecycle
- active
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Sources and related records
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