String jsonStr = '{ "oktaToken":"eyJraWQiOiIyNlN1NHFMNnVVZTVJX2M5X2Z3WmZvX09ON0dNUHRtQzlEeHFsTGplLS00IiwiYWxnIjoiUlMyNTYifQ.eyJ2ZXIiOjEsImp0aSI6IkFULlVINmdIOF9BcWJ" }';
Map<String, String> m = (Map<String, String>) JSON.deserialize(jsonStr, Map<String, String>.class);
String oktaToken = m.get('oktaToken');
System.debug(oktaToken);
Hope this helps!
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