APEX: Integration from internal pbx to Salesforce

Question

I am looking to create an app for AppExchange in Salesforce The goal is to login to my PBX and enable click_and_dial Actually I have this code:

<apex:page standardController="Contact" extensions="ClickAndDial" action="{!clickAndDial}">
    <apex:form >
        <apex:inputHidden value="{!contact.Id}"/>
        <apex:inputHidden value="{!contact.Phone}"/>
    </apex:form>
</apex:page>`

public  class ClickAndDial {
    public String Phone {get; set;}
    public Id Id { get; set; }
    public Contact contact { get; set; }
    public ClickAndDial(ApexPages.StandardController controller) {
        contact =  (Contact) controller.getRecord();
        Id = contact.Id;
        System.debug('The case record: ' + contact);
        Phone = contact.Phone;
    }

    ....

    public PageReference clickAndDial() {
        PageReference pageRef = new PageReference('/' + Id);
        HTTPRequest loginRequest = new HTTPRequest();
        loginRequest.setEndpoint('callout:SalesforceNC/services/data/v32.0');
        System.debug('Case Owner: ' + Phone);
        System.debug('Case Id: ' + Id);
        Http http = new Http();
        HttpRequest request = new HttpRequest();
        request.setMethod('POST');`
      request.setEndpoint('https://somendpoint');
        request.setHeader('Content-Type', 'application/x-www-form-urlencoded'); 
        String payload = 'token=' + EncodingUtil.urlEncode('pbx_login_token','UTF-8') + '&data='+EncodingUtil.urlEncode('my_data','UTF-8');
        request.setBody(payload);
        HttpResponse response = http.send(request);
        return pageRef;
    }
}

I need user login token to be able to call API How can I store user's PBX credentials and then retrieve them from clickAndDial method in order to perform login on PBX?