fix cookie expiration issue when exp claim is zero

[livetocode]

Hi,

Thanks for your excellent work!

I've encountered an issue with an infinite redirect loop after authentication which I tracked down to being caused by session cookies having 1970-01-01T00:00:00Z expiration dates.
After more digging, this was caused by the refresh token emitted by Keycloak which had a "exp" claim set to zero!

{
"jti": "f6bdb3b4-409f-43d1-9675-24ab06404c9a",
"exp": 0,
"nbf": 0,
"iat": 1525834984,
"iss": "https://example.com/auth/realms/hello",
"aud": "kubernetes",
"sub": "a7c5ce69-657e-45a2-9904-3cb85d51be36",
"typ": "Offline",
"azp": "kubernetes",
"nonce": "35e9f093d45483d1857c2e82c81fee51",
"auth_time": 0,
"session_state": "ba2e7a6f-985d-4647-b497-cb6e05809e3d",
"realm_access": {
"roles": [
"offline_access",
"uma_authorization"
]
},
"resource_access": {
"account": {
"roles": [
"manage-account",
"manage-account-links",
"view-profile"
]
}
}
}

Then the time difference time.Until(ident.ExpiresAt) was producing a negative duration, which caused the cookie to be in the 70', which of course prevented the browser from keeping it, thus causing the infinite loop.

Hope this helps,

Morgan

[gambol99]

LGTM ... much appreciated @livetocode