Hi Yavuz,
You have to create a client Id and Secret for every SharePoint Provider Hosted App, but you can use the same security certificate.
Probably you already know this but to achieve the client id and secret you have to go on the following SharePoint URL:
http://<SharePointWebsite>/_layouts/15/AppRegNew.aspx
like described here:
https://msdn.microsoft.com/en-us/library/office/jj687469.aspx?f=255&MSPPError=-2147217396
Kind regards
Giuliano De Luca - MCSD SharePoint, MCSD Web Applications, MCPS, MS. www.delucagiuliano.com Twitter: @giuleon