Here are the settings you need to connect to SuccessFactors:

API URL: e.g. https://apisalesdemo8.successfactors.com - see this for more info on identifying your URL - SAP SuccessFactors URLs

OnLink supports both Basic and OAuth authentication mechanisms to connect to SuccessFactors.

Basic Auth:

API Username: format is username@company_id, provide user access via: Admin Center >> Manage Permission Roles >> Manage Integration Tools >> Enable Allow Admin to Access OData API through Basic Authentication. OnLink requires access to these entities: User, UserAccount, EmpJob, EmpEmployment, EmpEmploymentTermination, PerPerson, PerEmail. See this link for instructions on finding your Company ID.
API Password: <api user’s password>

OAuth:

Public and Private Keys - Create key pair using openssl command described here - create certificate. Copy the public and private keys from this step. $ openssl req -nodes -x509 -sha256 -newkey rsa:2048 -keyout private.pem -out public.pem
Client ID - Register OAuth2 client application - register application. Copy the API Key.
Company ID - see this link for instructions on finding your Company ID.
User ID - user id of a technical user who has the right permissions to access OData API

To confirm your OAuth credentials are valid, you can use this blog to test with a third party tool.

SuccessFactors Webhook

SAP SuccessFactors API