Cargo "failed to authenticate" for a private git dependency in CI

By Daniel Zoghalchali·Latchkey

Cargo tried to fetch a git dependency from a private repository and the host rejected the request. Either no credentials were provided to CI, or a transient network failure interrupted the authenticated fetch.

What this error means

The build fails with error: failed to authenticate when downloading repository and a hint about SSH agent / credential helpers. Auth-config failures are deterministic; network drops pass on retry.

cargo

error: failed to get `internal-lib` as a dependency of package `app`

Caused by:
  failed to authenticate when downloading repository: git@github.com:org/internal-lib.git
  if the git CLI succeeds then `net.git-fetch-with-cli` may help here

Diagnose it: toolchain, features, or a stale target dir?

Cargo failures that only appear in CI are usually a different toolchain channel, a different feature set resolved by the dependency graph, or a target directory restored from a cache built with different flags.

Terminal

rustc --version --verbose
cargo --version
cat rust-toolchain.toml 2>/dev/null

# which features actually got enabled across the graph?
cargo tree -e features | head -40

# rule out a poisoned cache before anything else
cargo clean && cargo build --locked

Common causes

No credentials available to CI

The runner has no deploy key, token, or git credential helper configured, so the private host rejects the fetch.

Transient git host network drop

A momentary connectivity failure to the git host interrupts an otherwise-authenticated fetch.

How to fix it

Provide credentials and use the git CLI

Configure a token-based fetch and let cargo shell out to git.

.github/workflows/ci.yml

git config --global url."https://x-access-token:${TOKEN}@github.com/".insteadOf "https://github.com/"
export CARGO_NET_GIT_FETCH_WITH_CLI=true
cargo fetch --locked

Raise git retries for transient drops

Terminal

export CARGO_NET_RETRY=10
cargo build --locked

How to prevent it

Inject a least-privilege token or deploy key for private git deps.
Set CARGO_NET_GIT_FETCH_WITH_CLI=true so cargo reuses the configured git auth.
On self-healing managed runners (Latchkey), transient git-host network failures are auto-retried and the registry/git cache is preserved, so a flaky fetch does not fail the build.

Frequently asked questions

What causes Cargo "failed to authenticate" for a private git dependency in CI?

There are 2 common causes: no credentials available to ci and transient git host network drop. The runner has no deploy key, token, or git credential helper configured, so the private host rejects the fetch.

How do I fix Cargo "failed to authenticate" for a private git dependency in CI?

There are 2 fixes depending on which cause you have: provide credentials and use the git cli and raise git retries for transient drops. Work through them in order, since the first is the most common.

What does Cargo "failed to authenticate" for a private git dependency in CI actually mean?

The build fails with error: failed to authenticate when downloading repository and a hint about SSH agent / credential helpers.

How do I stop Cargo "failed to authenticate" for a private git dependency in CI happening again?

Inject a least-privilege token or deploy key for private git deps. The prevention section lists 3 changes that keep it from recurring.

Can Latchkey fix this automatically?

Yes. Latchkey runs your GitHub Actions on managed runners that detect this failure, apply the fix, and retry the job automatically - self-healing is on by default.