Description
This article describes how to troubleshoot authentication failures due to 'clock skew' SAML errors.
Scope
FortiOS 7.0.4 and later
Solution
1) The SAML Assertion from SAML IDP is only valid for a specific duration which is declared in the 'Assertion'.
If the clock on FortiGate and SAML IDP is not in sync, then this constraint will not be satisfied which causes the authentication to fail with below errors in SAML debugs
__samld_sp_login_resp [859]: Clock skew tolerance: 0
__samld_sp_login_resp [864]: Clock skew issue.
2) To fix this issue, make sure that time is in sync between FortiGate and the IDP.
3) In some cases, where the time sync between the FortiGate and IDP can not be controlled, 'clock-tolerance' can be configured to control how many seconds can be the difference between SP (FortiGate) and IDP as below:
# config user saml
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set clock-tolerance <in seconds> ( 0-300, 15 by default)
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