Trying to get Stack Overflow Access token Using "RestAssured"

Question

I have been trying to create an access token for a Stack Exchange app (already created). I am not even sure if I am using the correct URL https://stackoverflow.com/oauth/access_token.

RestAssured.given().auth().preemptive().basic(<My Client Id>,<My Client Key>)   
                      .formParam("grant_type", "client_credentials")
                      .formParam("scope", "")
                      .when()     .post("https://stackoverflow.com/oauth/access_token");

I am getting the below error

javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path validation failed: java.security.cert.CertPathValidatorException: timestamp check failed at sun.security.ssl.Alerts.getSSLException(Unknown Source) at sun.security.ssl.SSLSocketImpl.fatal(Unknown Source) at sun.security.ssl.Handshaker.fatalSE(Unknown Source) at sun.security.ssl.Handshaker.fatalSE(Unknown Source) at sun.security.ssl.ClientHandshaker.serverCertificate(Unknown Source) at sun.security.ssl.ClientHandshaker.processMessage(Unknown Source) at sun.security.ssl.Handshaker.processLoop(Unknown Source) at sun.security.ssl.Handshaker.process_record(Unknown Source) at sun.security.ssl.SSLSocketImpl.readRecord(Unknown Source) at sun.security.ssl.SSLSocketImpl.performInitialHandshake(Unknown Source) at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source) at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source) at