argocd login fails: x509: certificate signed by unknown authority

The Argo CD server presents a self-signed (or private-CA) certificate your machine does not trust - TLS verification fails before any credential is sent. For labs, argocd login --insecure skips verification; for anything real, add the server's CA to the system trust store (or pass the CA properly) instead of training yourself to ignore TLS.

The error

FATA[0000] x509: certificate signed by unknown authority

What to do

1. Lab-only quick path:

argocd login [server] --insecure --username [user]

Expected: Login succeeds with verification skipped.

2. Proper fix: fetch the server CA and add it to the OS trust store (Linux: /usr/local/share/ca-certificates + update-ca-certificates; macOS: Keychain). Expected: System trusts the CA.

3. Log in normally:

argocd login [server] --username [user]

Expected: Succeeds without --insecure.

When this applies

• the exact x509: certificate signed by unknown authority message
• self-signed Argo CD installs
• private-CA corporate environments

When it does NOT apply

• certificate expired (different x509 message - renew the cert)
• hostname mismatch (cert valid, wrong name - fix DNS or the cert)

Works with

argocd CLI 2.x/3.x

x509: certificate has expired or is not yet valid

Clock skew or an actually expired cert. Check date on both ends, then renew.

Why it happens

argocd-server generates a self-signed cert at install unless you provide one. The CLI verifies TLS like any HTTPS client, and an unknown CA fails the handshake.

Edge cases

• --insecure is stored per context; teammates copying your config inherit the skip - document it.
• Some setups terminate TLS at the ingress with a public cert - then this error means you are hitting the wrong endpoint.

Resolved from

computingforgeeks argocd login guide - https://computingforgeeks.com/argocd-cli-login-authentication/

Asked: argocd login fails with x509: certificate signed by unknown authority on a fresh install. Verified answer: Use --insecure for labs; install the server CA into the system trust store for real use. Source: https://computingforgeeks.com/argocd-cli-login-authentication/ (thread computingforgeeks argocd login guide). Tool: argocd-cli.