I configured a OIDC identity provider by selecting the OpenID Connect v1.0 identity provider from the drop-down box on the top right corner of the identity providers table in Keycloak's Admin Console. During the configuration process, I also configure "Logout Url" for the IDP logout url. 

When I try to logout to the external IDP, the browser is redirected to the external IDP to perform the logout. I can see some URL as follows:

https://keycloakdev.xxxxxxx.com/auth/realms/Internal/protocol/openid-connect/logout?state=a4efbda0-8b98-4169-a369-59e92bc3fac5&id_token_hint=eyJhbGciOiJSUzI1NiJ9.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.BIneKvUpSPq4c32dV5JclWPjtbA0U55u8Pf_C7KDokNMMBKCERHnzIS8-9csBxh8NLJbB_PmApMY0raAz-YPOcwyvmsOJ23bSrDR3Oa2HZ5JEGzs9IVFyhzQXJuDBCBWcPZl-eNxnxdGkNJBd7Cx03iWsUVUE9NeJYPjeZ5s8rmDtaX38V6JywugWRby5rfSZDLpu7xoGj6a_ZSZEXUfktwCMHS0Jnz_1M778Bmka0TcD1bvIpuqVl4-YQf2P3UZWgxqFQoNDVegZUNuekqUQyJiuRjlQuhITg5tDYfy2DbhkqVsN2gR7mUp21WNx2S5pG5Hb9cXajIVGR6SmW4qKA:

"keycloakdev.xxxxxxx.com" is where the externalIDP is located. "Internal" is the name of the realm. The parameters "state" and "id_token_hint" are appended to the endpoint logout URL automatically during the logout process.   

However, this process failed because I got "Session Not Active" error in the UI. After some investigations, I found this "Session Not Active" error seems to be related to the value of Realm Setting —> Tokens —> Access Token Lifespan I configured. The default value is 5 minutes, if I trigger the logout within 5 minutes, I can logout to the external IDP successfully. If I do the logout after 5 minutes, I will get this ""Session Not Active" error. Is this the expected behavior?  Do I have to bump up the value of "Access Token Lifespan" to get a longer session for the logout purpose? 

Thanks a lot for the help!

Xiao