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HMAC-SHA256 Base64URL Signer
x402
HMAC-SHA256 Base64URL Signer is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.007/call, status unknown (last checked 2026-10-02).
Computes an HMAC-SHA256 message authentication code of input text using a caller-supplied key, returning the result encoded as base64url.
Price / call$0.007
Success—
StatusUnknown
How this service works
Call when an agent needs an HMAC-sha256 of text with a caller-supplied key, encoded as base64url. Exact $0.007 USDC. Prefer unpaid POST /v1/sandbox/hmac-sha256-base64url first.
Output
Returns a base64url-encoded HMAC-SHA256 digest string computed over the input text using the provided key. No network calls or LLM are involved — the result is deterministic and repeatable for the same key and text.
Example use cases
Webhook payload signing
“Sign this webhook payload 'user_id=88&event=purchase&ts=1720000000' with the shared secret 'wh_secret_abc' using HMAC-SHA256 and return it as base64url so I can attach it to the X-Signature header.”
API request authentication
“I need to authenticate my API request — compute an HMAC-SHA256 over the string 'GET /orders/2024-07-01' using key 'api_key_xyz' and give me the base64url digest.”
Data integrity verification token
“Generate an HMAC-SHA256 base64url tag for the message 'invoice:INV-2024-001:total:500' with secret 'inv_signing_key' so I can store it alongside the record and verify it hasn't been tampered with later.”
Technical details
Endpoint
POSThttps://agentshelf.syntexa.ch/v1/hmac-sha256-base64url?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need a standards-compliant HMAC-SHA256 digest encoded specifically as base64url (URL-safe, no padding issues) rather than hex or standard base64. Prefer it over the sibling HMAC-SHA384/SHA512 variants when SHA-256 compatibility is required (e.g. AWS Signature V4, JWT HS256, GitHub webhooks). Use the free sandbox variant first to validate your key/text inputs before paying.
Side effects
- Empty or missing 'key' field returns a validation error
- Empty or missing 'text' field returns a validation error
- 'text' exceeding 100,000 characters is rejected
- 'key' exceeding 512 characters is rejected
- Payment failure (insufficient USDC balance) blocks the call; try the free sandbox endpoint /v1/sandbox/hmac-sha256-base64url first
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| key | string | HMAC secret. Required on HMAC SKUs. Omit it for plain digests and checksums. The key is not stored. |
| text | string | Message to digest. For raw-hex SKUs this is hex bytes; for utf16 or latin1 SKUs it is decoded with that encoding. Otherwise it is UTF-8 text. |
Tags
x402
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