Security Groups & Permission level

We have a requirement of creating security policy in SharePoint as follows:-

1) We would like to create a Security Policy

2) Add users and groups in the security policy

3) Assign permission levels to the users and groups who are added in the security policy (permission level can be different for a user and different for a group even both are in the same security policy)

4) Assign the security policy on a document or any item in SharePoint, accordingly the security privileges should be applied as defined in the security policy) 

Please suggest some solution how can we achieve above

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