Explore Mercury’s Authorization Schema in this example, delving into the intricate interplay among users, organizations, and accounts. Uncover the defined user roles, approval workflows, and limits, providing a snapshot of the dynamic relationships within the Mercury ecosystem.

For those who don’t know, Mercury is a bank offering both checking and savings accounts, complete with debit and credit card features. Given the delicate nature of financial transactions, Mercury has built-in access control features to ensure security.

But today we’re going to focus on approvals. Mercury allows it’s users to set a number amount for multiple user approval for any action.

For instance, an admin can decide that withdrawals above $1000 by members require approval from two designated approvers.

This means, if a member wants to withdraw more than $1000, they need a green light from two admin. And if an admin tries to withdraw they need an approval form another admin.

  • Admin → Withdraw $1000 → needs an approver
  • Member → Withdraw $1000 → needs 2 approvers.

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Full Schema | Open in playground

So let’s start with building basics. We need Users, Organization, Accounts both Savings and Deposits as entities in the mercury

entity user {}

entity organization {}

entity teams {}

entity accounts {}

Then inserting relations into these entities.

entity user {}

entity organization {
	relation admin @user
	relation member @user
}

entity accounts {
	relation checkings @accounts
	relation savings @accounts

	relation org @organization
}

Next step is to define actions in our use case.

entity user {}

entity organization {
    relation admin @user
    relation member @user
}

entity account {

    relation checkings @account
    relation savings @account

    relation org @organization

    action withdraw =

}

Now we need to define our attributes which will help us create access rights via Withdraw Limit and Admin Approval of the account.

Every organization has a set withdrawal limit. Additionally, for members and admins of the organization, there are specific approval limits in place when they attempt to withdraw amounts exceeding this limit.

entity user {}

entity organization {
    relation admin @user
    relation member @user
}

entity account {

    relation checkings @account
    relation savings @account

    relation org @organization

    attribute approval integer
    attribute balance double

    action withdraw =

}

Let’s create our rules that defines our attribute-based access rights.

  • Balance of the account must be more than withdraw amount
  • If withdraw amount is less than the withdraw limit we don’t need approval
  • Else; we need approve of two admins if we’re member, and we need approve of single admin if we’re another admin.
entity user {}

entity organization {
    relation admin @user
    relation member @user

    attribute admin_approval_limit integer
    attribute member_approval_limit integer
    attribute approval_num integer

    action approve = admin
    action create_account = admin

    permission approval = (member and check_member_approval(approval_num, member_approval_limit)) or (admin and check_admin_approval(approval_num, admin_approval_limit))
}

entity account {
    relation checkings @account
    relation savings @account

    relation owner @organization
    
    attribute withdraw_limit double
    attribute balance double 

    action withdraw = check_balance(balance, request.amount) and (check_limit(withdraw_limit, request.amount) or owner.approval)
}

rule check_balance(balance double, amount double) {
    balance >= amount
}

rule check_limit(withdraw_limit double, amount double) {
    withdraw_limit >= amount 
}

rule check_admin_approval(approval_num integer, admin_approval_limit integer) {
    approval_num >= admin_approval_limit
}

rule check_member_approval(approval_num integer, member_approval_limit integer) {
    approval_num >= member_approval_limit
}

At last, as you can see we use the Rules to define access rights to withdraw which basically translates into;

  • Check balance if it’s over the withdraw amount. If not don’t allow the action.
  • Check withdraw limit; if it’s less than the limit allow the action…
  • Else;
    • Check if user is admin, and have approval more than the approval limit for admins.
    • Check if user is member, and have approval more than the approval limit for members.

​
Need any help ?

This is the end of demonstration of the authorization structure for Facebook groups. To install and implement this see the Set Up Permify section.

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