Hello, I am new to Integrations/ SOAP API, so apologize if this is an elementary question. I received documentation on how to fill the body of the http request, but I realize that I also need to add authorization into the request. I have the key and secret, but I don't know where to put that in the code. 
1. Where would I put it in the request?
2. What would the key/value pair look like in the JSON? 
Here is what my request looks like so far:

       public Object  makePostCallout() {
    Lead ref =[Select Id, firstname, lastname, gender__c, patient_dob__c, patient_ssn__c from Lead where Id = :ApexPages.currentPage().getParameters().get('id')]; 
           system.debug('***NAME OF REFERRAL***: '+ ref.firstname + ' ' + ref.lastname);
    String ssnReplace; 
           if (ref.Patient_SSN__c != null){
            ssnReplace = ref.Patient_SSN__c.replace('-','');
           }
    String genderLetter;
           if (ref.Gender__c == 'Male'){
               genderLetter = 'M';
           } else if (ref.Gender__c == 'Female'){
               genderLetter = 'F';
           }
           
           String first;
           String second;
           String third;
            String d = String.valueOf(ref.Patient_DOB__c);
           system.debug('***dob string raw: ' + d);
                first = d.substring(0,4);
                second = d.substring(5,7);
                third = d.substring(8,10);
           String dob = first + second + third;
           system.debug('***dob formatted: ' + dob);
           
           Map<string, string> patientInfoMap = new Map<string, string>();
                          patientInfoMap.put('social_security_number', ssnReplace);
                          patientInfoMap.put('birthdate', dob);
                          patientInfoMap.put('gender', genderLetter);
                          patientInfoMap.put('last_name', ref.lastname);
                          patientInfoMap.put('first_name', ref.firstname);
           List<Object> patientInfoList = new List<Object>();
           patientInfoList.add(patientInfoMap);
           
           JSONGenerator gen = JSON.createGenerator(true);   
            gen.writeStartObject();     
             gen.writeStringField('processing_mode', 'Realtime');
             gen.writeStringField('request_type', '270');
             gen.writeStringField('information_source_id', '1');
             gen.writeStringField('submitter_system_id', '2');
             gen.writeStringField('submitter_system_type', 'api');
             gen.writeStringField('submitter_request_id', 'R1');
                 gen.writeStringField('submitter_user_id', '99');
            gen.writeObjectField('subscribers', patientInfoList);
              gen.writeEndObject();   
         String jsonS = gen.getAsString();
        System.debug('***jsonMaterials***'+jsonS);
          
       // Continuation con = new Continuation(40);
        //con.continuationMethod='processResponse';

       HttpRequest req = new HttpRequest();
        req.setEndpoint('https://...(left out)');
        req.setMethod('POST');
        req.setBody(jsonS);
       Http http = new Http();  
       //  this.requestLabel = con.addHttpRequest(req);
     HTTPResponse res = http.send(req);
      // return con; 
           
  String result = null;
    Integer statusCode = res.getStatusCode();
          system.debug('***statusCode is***: ' + statusCode);
   if(statusCode == 200){
             system.debug('***API invoked successfully***');
    result = res.getBody();
          system.debug('***RESULT***: ' + result);
      }   
           return result;   
        
    }