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SEC_E_CERT_UNKNOWN
SEC_E_CERT_UNKNOWN signals this condition: SSPI could not complete processing of a certificate used in authentication. This is a generic certificate-processing failure. The actionable cause is usually an earlier chain, revocation, EKU, private-key, or identity-mapping error in the authentication logs.
What to check
- Inspect the certificate chain and the event that first reported validation failure.
- Verify that the intended certificate has the required usage and can access its private key in the current context.
- Do not import a certificate solely to make the error disappear; establish the expected issuing CA and identity mapping first.
Microsoft: Smart-card certificate requirements
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