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October 3, 2026 | GitHub Apps / credential handling

Your token got longer. Your contract did not.

GitHub App installation tokens moved from about 40 characters to about 520. The prefix stayed. The permissions and one-hour lifetime stayed. Every length assumption in between now gets a real test.

A credential is an opaque value with a scope and an expiry. Its character count is packaging, not identity.
Token envelope fixture13x length change
The prefix is not the contract.Test every store, header, proxy, log filter, and renewal path with the new envelope.

The quiet break is a fixed width.

GitHub completed its staged rollout of stateless installation access tokens on October 2. New tokens still begin with ghs_, but GitHub says they are now about 520 characters long instead of 40.[1] Code that asks only whether a value starts with ghs_ may pass. A database column, secret store, environment handoff, proxy, or redaction rule can still clip the rest.

GitHub says repository scope, permissions, the one-hour expiration, and the token endpoint did not change.[1] That makes this a useful compatibility lesson. The meaning stayed stable while the serialized value changed shape.

If a secret parser knows the length, it knows too much.

Read the response, not the string.

The installation-token endpoint returns the token with its expiry, permissions, and repository access. Callers may narrow repositories and permissions when they mint it. They cannot grant more access than the installation already has.[2]

Those response fields belong in your control record. The token itself does not. Treat it as a bearer credential, keep it out of URLs and logs, use transport security, and limit its exposure.[3] A longer token does not need decoding by every service that forwards it.

Fix the whole handling route.

GitHub calls out four failure points: exact-length validation, fixed or small storage, intermediaries that reject long authorization headers, and redaction patterns written for the old format.[1] Add renewal and expiry handling to the test plan. A one-hour token needs a controlled refresh path even when its format is accepted.

GitHub's app guidance also recommends minimum permissions, secure secret storage, and the correct token type for the actor.[4] Format compatibility does not replace access review.

Run a synthetic envelope test.

  1. Mint a test installation token in a non-production installation. Do not copy it into tickets or chat.
  2. Pass it through the same storage, process environment, proxy, and request library used in production.
  3. Confirm that logs and error reports redact the entire value. Test both the former and current lengths.
  4. Call one low-risk endpoint allowed by the test installation. Record only the response status, installation, scope, and expiry.
  5. Let the token expire. Confirm that the renewal path replaces it without printing either credential.
  6. Remove the temporary format-override header before GitHub's November 30, 2026 deprecation date.

The migration is done when the route handles an opaque credential. It is not done when one regular expression accepts 520 characters.

Interactive makeover / token envelope stretch bench

Find the 40-character assumptions.

Traditional purpose replaced: a loose migration checklist. Better version: select the token envelope, close each handling gate, watch the route fill, and copy a review packet that keeps live credentials out.

Envelope controls

Choose a synthetic length. No credential value enters the page.

Test fixture
Fixture length520 characters
Handling gates
Generated compatibility packet

See which boundary is untested

Selected means included in the test packet. It does not mean a production system passed.

Credential handling route0 of 4 gates selected
Test structure is open.Select the handling gates that the compatibility run must exercise.
All four selections make the test structure complete. The packet still needs a test installation, observed outputs, and a reviewer. It never stores a token.

Sources read

Source log and evidence boundary
  1. GitHub Changelog, "Stateless GitHub App installation tokens rolled out", published October 2, 2026 and read October 3, 2026. It supports the rollout status, old and new approximate lengths, unchanged scope and expiry, migration failure points, and November 30 header deprecation date.
  2. GitHub Docs, "Generating an installation access token for a GitHub App", read October 3, 2026. It supports the token endpoint flow, one-hour expiry, optional repository and permission narrowing, and response fields.
  3. RFC 6750, "The OAuth 2.0 Authorization Framework: Bearer Token Usage", read October 3, 2026. It supports authorization-header transport, TLS, short lifetimes, and the warning against putting bearer tokens in URLs.
  4. GitHub Docs, "Best practices for creating a GitHub App", read October 3, 2026. It supports minimum permissions, secure credential storage, repository and permission narrowing, and choosing installation versus user tokens by actor.

Evidence boundary. This page teaches a compatibility test and generates a blank packet. It does not connect to GitHub, create a token, validate an installation, inspect a proxy, read logs, or prove that any system handles the new format.