You can retrieve the access token with the command below.
curl -X POST -H "Content-Type:application/x-www-form-urlencoded" <oauth2-token-url> --insecure --data "client_id=<client-id>&client_secret=<client-secret>&grant_type=client_credentials&scope=openid"
curl -X POST -H "Content-Type:application/x-www-form-urlencoded" https://localhost:9443/oauth2/token --insecure --data "client_id=1Kfz8ivbw0hqjoTbo1LbVTJl2f4a&client_secret=8c7d2hVE4p17_lIZ4FHOtWLJfQEa&grant_type=client_credentials&scope=openid"
{"scope":"openid","token_type":"bearer","expires_in":3300,"id_token":"eyJhbGciOiJSUzI1NiJ9.eyJhdXRoX3RpbWUiOjE0MzAzODkyNjEyOTIsImV4cCI6MTQzMDM5Mjg2MTI5Miwic3ViIjoiYWRtaW4iLCJhenAiOiIxS2Z6OGl2YncwaHFqb1RibzFMYlZUSmwyZjRhIiwiYXRfaGFzaCI6IlkyUXlNMk5pWTJNMFlqWXpZell4WkdKaE5HVmxNR0ZtTVRJNU1UUXpOZz09IiwiYXVkIjpbIjFLZno4aXZidzBocWpvVGJvMUxiVlRKbDJmNGEiXSwiaXNzIjoiaHR0cHM6XC9cL2xvY2FsaG9zdDo5NDQzXC9vYXV0aDJlbmRwb2ludHNcL3Rva2VuIiwiaWF0IjoxNDMwMzg5MjYxMjkyfQ.DC9jDagCCkOXYD4ZVF-9wNpddoTdH96B7Mw_3nGv-2lW9SiWvL600b4Cch2mNoFAao1QeGl9pAP4bvbVgJGuthunQxBJuTYLy2KCH5k5Hc9lQsZtEM5Z6yzQ7q2wWfu9il9Lya-gUXVnBJEd5ovqtwI40KSLvuZUoei7l3S8lZo","access_token":"cd23cbcc4b63c61dba4ee0af1291436"}
curl -k -H "Authorization: Bearer <access-token>" <userinfo-edpoint>?schema=openid
curl -k -H "Authorization: Bearer 7244fef5b5de362489c5b2ed16de9e" https://localhost:9443/oauth2/userinfo?schema=openid
{"name":"admin","family_name":"admin","preferred_username":"admin","given_name":"admin"}