Salesforce Integration with Linkedin

1. Create developer account in linkedin Account.
2. Create connected application in linkedin 
3. develop the code in salesforce environment
     i) create a custom object to store the token information
     ii) add remote site settings
     iii) test the integration

Create developer account in linkedin Account:
Type https://developer.linkedin.com in URL and click enter you will redirect to below page

Note: Create a visualforce page for redirect URI and save in connected app like https://munna550-dev-ed--c.ap5.visual.force.com/apex/LinkedinResponse

<apex:page controller="Rest_OAuth_LinkedIN" action="{!readcode}">
    {!code}
</apex:page>

Creating a custom object in salesforce and clientID, clientsecret and redirect uri in that object as shown below.

Request for code from Linkedin:
public class Rest_OAuth_LinkedIN {
    public string accestoken {set; get;}
    public string code {set; get;}
    public Serverdata__c data {set; get;}
    public Rest_OAuth_LinkedIN(){
        data = [select Client_ID__c, Client_Secret__c, Redirect_URL__c from Serverdata__c where Name = 'LinkedIN'];
    }
    /* Request for code
     * endpoint url  : https://www.linkedin.com/oauth/v2/authorization
     * Method        : GET
     * parameters    : response_type = code
     *               : client_id = connected app clientid
     *               : redirect_uri = connected app redirecturi
     *               : state = any random string
     */
   public void readcode(){
            code=Apexpages.currentPage().getparameters().get('code');   
        }
    public PageReference requestcode(){
        string endpoint='https://www.linkedin.com/oauth/v2/authorization?';
        endpoint=endpoint+'response_type=code';
        endpoint=endpoint+'&client_id='+data.Client_ID__c;
        endpoint=endpoint+'&redirect_uri='+data.Redirect_URL__c;
        endpoint=endpoint+'&state=shaik';
        PageReference p = new PageReference(endpoint);
        return p;
    }
}

Create a visualforce home page to send a request through button to linkedin, we will get code as shown below:

<apex:page controller="Rest_OAuth_LinkedIN">
    <apex:form>
       <apex:commandButton value="code" action="{!requestcode}"/>
    </apex:form>
</apex:page>

Request for Access Token:
public class Rest_OAuth_LinkedIN {
    public string accesstoken {set; get;}
    public string code {set; get;}
    public Serverdata__c data {set; get;}
    public Rest_OAuth_LinkedIN(){
        data = [select Client_ID__c, Client_Secret__c, Redirect_URL__c from Serverdata__c where Name = 'LinkedIN'];
    }
    /* Request for code
     * endpoint url  : https://www.linkedin.com/oauth/v2/authorization
     * Method        : GET
     * parameters    : response_type = code
     *               : client_id = connected app clientid
     *               : redirect_uri = connected app redirecturi
     *               : state = any random string
     */
    public void readcode(){
            code=Apexpages.currentPage().getparameters().get('code');   
        }
    public PageReference requestcode(){
        string endpoint='https://www.linkedin.com/oauth/v2/authorization?';
        endpoint=endpoint+'response_type=code';
        endpoint=endpoint+'&client_id='+data.Client_ID__c;
        endpoint=endpoint+'&redirect_uri='+data.Redirect_URL__c;
        endpoint=endpoint+'&state=shaik';
        PageReference p = new PageReference(endpoint);
        return p;
    }
    /* Request for acesstoken
     * endpoint url  : https://www.linkedin.com/oauth/v2/accessToken
     * Method        : POST
     * Parameters    : grant_type=authorization_code
     *               : code=The authorization code you received from above
     *               : redirect_uri = from connected app
     *               : client_id = from connected app
     *               : client_secret = from connected app
     */
    public void requestToken(){
        string endpoint='https://www.linkedin.com/oauth/v2/accessToken';
        string body='grant_type=authorization_code';
        body=body+'&code='+code;
        body=body+'&redirect_uri='+data.Redirect_URL__c;
        body=body+'&client_id='+data.Client_ID__c;
        body=body+'&client_secret='+data.Client_Secret__c;
        Http p = new Http();
        HttpRequest request = new HttpRequest();
        request.setEndpoint(endpoint);
        request.setMethod('POST');
        request.setBody(body);
        HttpResponse response = p.send(request);
        string result = response.getBody();
        System.JSONParser JP = JSON.createParser(result);
        while(JP.nextToken()!=NUll){
            if(JP.getText()=='access_token'){
                JP.nextToken();
                accesstoken = JP.getText();
            }
        }
    }
 }

<apex:page controller="Rest_OAuth_LinkedIN" action="{!readcode}">
    {!code}
    <apex:form>
       <apex:commandButton value="gettoken" action="{!requestToken}"/>
    </apex:form>
    {!accesstoken}
</apex:page>

Once we get access token, we supposed to get the details of the profile from LinkedIN:
public class Rest_OAuth_LinkedIN {
    public string accesstoken {set; get;}
    public string code {set; get;}
    public string result {set; get;}
    public Serverdata__c data {set; get;}
    public Rest_OAuth_LinkedIN(){
        data = [select Client_ID__c, Client_Secret__c, Redirect_URL__c from Serverdata__c where Name = 'LinkedIN'];
    }
    /* Request for code
     * endpoint url  : https://www.linkedin.com/oauth/v2/authorization
     * Method        : GET
     * parameters    : response_type = code
     *               : client_id = connected app clientid
     *               : redirect_uri = connected app redirecturi
     *               : state = any random string
     */
    public void readcode(){
            code=Apexpages.currentPage().getparameters().get('code');   
        }
    public PageReference requestcode(){
        string endpoint='https://www.linkedin.com/oauth/v2/authorization?';
        endpoint=endpoint+'response_type=code';
        endpoint=endpoint+'&client_id='+data.Client_ID__c;
        endpoint=endpoint+'&redirect_uri='+data.Redirect_URL__c;
        endpoint=endpoint+'&state=shaik';
        PageReference p = new PageReference(endpoint);
        return p;
    }
    /* Request for acesstoken
     * endpoint url  : https://www.linkedin.com/oauth/v2/accessToken
     * Method        : POST
     * Parameters    : grant_type=authorization_code
     *               : code=The authorization code you received from above
     *               : redirect_uri = from connected app
     *               : client_id = from connected app
     *               : client_secret = from connected app
     */
    public void requestToken(){
        string endpoint='https://www.linkedin.com/oauth/v2/accessToken';
        string body='grant_type=authorization_code';
        body=body+'&code='+code;
        body=body+'&redirect_uri='+data.Redirect_URL__c;
        body=body+'&client_id='+data.Client_ID__c;
        body=body+'&client_secret='+data.Client_Secret__c;
        Http p = new Http();
        HttpRequest request = new HttpRequest();
        request.setEndpoint(endpoint);
        request.setMethod('POST');
        request.setBody(body);
        HttpResponse response = p.send(request);
        string result = response.getBody();
        System.JSONParser JP = JSON.createParser(result);
        while(JP.nextToken()!=NUll){
            if(JP.getText()=='access_token'){
                JP.nextToken();
                accesstoken = JP.getText();
            }
        }
        getprofile();
    }
    public void getprofile(){
        string endpoint = 'https://api.linkedin.com/vi/people/~?format=json';
        Http p = new Http();
        HttpRequest request = new HttpRequest();
        request.setEndpoint(endpoint);
        request.setMethod('GET');
        request.setHeader('Authorization','Bearer '+ accesstoken);
        HttpResponse response = p.send(request);
        result = response.getBody();
    }
 }

<apex:page controller="Rest_OAuth_LinkedIN" action="{!readcode}">
    {!code}
    <apex:form>
       <apex:commandButton value="gettoken" action="{!requestToken}"/>
    </apex:form>
    {!result}
</apex:page>