American Express Authentication

generated: '2026-07-23'
method: searched
source: https://developer.americanexpress.com/documentation/api-security
docs:
  - https://developer.americanexpress.com/documentation/api-security/certificates
  - https://developer.americanexpress.com/documentation/api-security/hmac
  - https://developer.americanexpress.com/documentation/api-security/oauth-2
description: >-
  American Express developer APIs are onboarding-gated and secured with a
  layered scheme: mutual TLS (two-way client-certificate authentication),
  request-level HMAC message authentication (MAC) signatures, and OAuth 2.0
  bearer tokens for authorization. No public OpenAPI is published, so this
  profile is captured from the Amex for Developers API Security documentation
  rather than derived from a machine-readable spec.
summary:
  types: [mutualTLS, http, oauth2]
  api_key_in: []
  oauth2_flows: [clientCredentials]
schemes:
  - name: mutualTLS
    type: mutualTLS
    description: >-
      Two-way TLS. Partners are issued client certificates during onboarding and
      must present them on every API call; American Express validates the client
      certificate alongside the server certificate.
    docs: https://developer.americanexpress.com/documentation/api-security/certificates
  - name: hmac
    type: http
    scheme: hmac
    description: >-
      HMAC / Message Authentication Code (MAC) request signing. Each request
      carries an Authorization header containing an HMAC signature computed over
      the request using the partner's issued MAC ID and secret, protecting
      message integrity and authenticity.
    docs: https://developer.americanexpress.com/documentation/api-security/hmac
  - name: oauth2
    type: oauth2
    scheme: bearer
    description: >-
      OAuth 2.0 access tokens are used for authorization on APIs that require
      them; tokens are obtained via the Amex token endpoint and presented as
      bearer credentials. Scope and grant details are provisioned per partner
      onboarding.
    docs: https://developer.americanexpress.com/documentation/api-security/oauth-2
    flows:
      - flow: clientCredentials
notes:
  - Client SDKs (packages/american-express-packages.yml) implement the mTLS + HMAC
    request-signing so partners do not hand-roll the signature.
  - Access is partner-gated; credentials, certificates, and MAC secrets are issued
    during onboarding rather than self-service.