Hi,

please refer below links

https://docs.servicenow.com/bundle/newyork-application-development/page/integrate/outbound-rest/concept/c_OAuth2ProfileTutorialGoogle.html

https://docs.servicenow.com/bundle/orlando-application-development/page/integrate/outbound-rest/task/t_ConfigureARESTMessageWithOAuth.html

https://docs.servicenow.com/bundle/orlando-application-development/page/integrate/outbound-rest/concept/c_OutboundRESTAuth.html

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Regards
Ankur