Hi ,
I have a problem where i cannot place API requests to the user accounts which are professional editions (API not enabled for this organization issue) .After some searching i had found this document at this link 

https://developer.salesforce.com/docs/atlas.en-us.packagingGuide.meta/packagingGuide/dev_packages_api_access.htm

which explains some points as following :

• Currently, the standard Data SOAP and REST APIs are supported for GE and PE apps, and Metadata API is supported in PE apps. To request API access, see How do I get an API token for my app? You can also contact Salesforce to request that a connected app be whitelisted to use the REST API in GE or PE orgs.
• Other APIs, such as the Bulk API and Apex methods exposed as SOAP Web services, remain unavailable.
• You can enable REST-based Web services using connected app consumer whitelisting.
• You can enable SOAP-based Web services, including Metadata API, using an API token called a Client ID, which is appended to your SOAP headers in integration calls. This special key enables your app to make calls to GE and PE orgs for Data API and PE orgs for Metadata API, even if the customer does not have API access.

The bolded text above mention something about whitelisting a connected app.
So ,how can that be achieved ?