Resolved

X Twitter API returns 401 Unauthorized for media uploads with OAuth 1.0a

Python
API
OAuth
Authentication
Twitter API
Debugging
Security
Backend

OAuth 1.0a authentication failing for X/Twitter API v1.1 media upload endpoint | Returns 401 Unauthorized with code 32 despite valid credentials | Root cause in percent-encoding and signing key implementation

Issue

The X (Twitter) API v1.1 media upload endpoint was failing with 401 Unauthorized errors, despite valid credentials and proper endpoint configuration. After partial fixes, the error evolved into 403 Forbidden responses. The issue persisted even after confirming valid API keys, access tokens, and write permissions (up to 500 writes/month).

Culprit

Three key misconfigurations caused the authentication failures:

  1. Incorrect OAuth 1.0a Percent Encoding: The implementation used default percent encoding, which did not comply with OAuth 1.0a’s strict requirement to encode all characters in the signature base string, leading to HMAC-SHA1 signature mismatches.
  2. Double-Encoded Signing Key: The OAuth 1.0a signing key was incorrectly URL-encoded, violating the specification that requires raw secrets concatenated with &.
  3. Immutable Token Scope: The access token retained outdated read-only permissions even after updating the app’s permissions to include write access in the X Developer Portal, requiring token regeneration to inherit the new permissions.

Solution

The following adjustments resolved the authentication issues:

  1. Strict Percent Encoding: Ensured all characters in the signature base string were encoded without exceptions, adhering to OAuth 1.0a’s requirements.
  2. Raw Signing Key: Used unencoded secrets for the signing key, concatenated with &, to comply with the OAuth 1.0a specification.
  3. Authorization Header Encoding: Properly encoded values in the OAuth authorization header to prevent validation failures.
  4. Permission and Token Regeneration: Updated the X Developer Portal to include write permissions and configured a callback URI. Regenerated access tokens to ensure they inherited the new write permissions.
  5. Validation: The fix successfully produced a 202 Accepted response from the API, confirming the resolution of the authentication issues.

Key Insight: OAuth 1.0a imposes three distinct encoding contexts—signature base strings, signing keys, and authorization headers—each requiring careful handling to avoid signature validation failures.