How to get session id in Salesforce?

1. Use POST method.

2. Set the end point.

Sandbox - https://test.salesforce.com/services/Soap/u/35.0
Production - https://login.salesforce.com/services/Soap/u/35.0

Use custom domain URL if my domain is enabled and prevent login from test or login.salesforce.com is enabled.

3. Set your headers as below.

SOAPAction = ""
Content-Type = text/xml

4. Use the below as body.

1. <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:urn="urn:partner.soap.sforce.com">  
2.   
3.    <soapenv:Body>  
4.   
5.       <urn:login>  
6.   
7.          <urn:username>Login ID</urn:username>  
8.   
9.          <urn:password>Password</urn:password>  
10.   
11.       </urn:login>  
12.   
13.    </soapenv:Body>  
14.   
15. </soapenv:Envelope>  

5. Get the SessionId.