public double loginRefreshWindowFactor() {
        return loginRefreshWindowFactor;
    }
Background login refresh thread will sleep until the specified window factor
relative to the credential's total lifetime has been reached, at which time
it will try to refresh the credential.

@return the login refresh window factor
clients/src/main/java/org/apache/kafka/common/security/oauthbearer/internals/expiring/ExpiringCredentialRefreshConfig.java