Frequently Asked Questions

How do I make user attributes stored in LDAP/AD available to OPA for making decisions?

This best-practice guide explains three options: JSON Web Tokens, synchronization with LDAP/AD, and calling into LDAP/AD during policy evaluation.

How does OPA do conflict resolution?

In Rego (OPA's policy language), you can write statements that both allow and deny a request, such as

package foo
allow { input.name = "alice" }
deny { input.name = "alice" }

Neither allow nor deny are keywords in Rego so if you want to treat them as contradictory, you control which one takes precedence explicitly. When you ask for a policy decision from OPA, you specify both the policy name (foo) and the virtual document that names the decision within foo. Typically in this scenario, you create a virtual document called authz and define it so that allow overrides deny or vice versa. Then when asking for a policy decision, you ask for foo/authz.

# deny everything by default
default authz = false

# deny overrides allow
authz {
    allow
    not deny
}

If instead you want to resolve conflicts using a first-match strategy (where the first statement applicable makes the decision), see the FAQ entry on statement order.

Does Statement Order Matter?

The order in which statements occur does not matter in Rego. Reorder any two statements and the policy means exactly the same thing. For example, the following two statements mean the same thing whichever order you write them in.

ratelimit = 4 { input.name = "alice" }
ratelimit = 5 { input.owner = "bob" }

Sometimes, though, you want the statement order to matter. For example, you might put more specific statements before more general statements so that the more specific statements take precedence (e.g. for conflict resolution). Rego lets you do that using the else keyword. For example, if you want to make the first statement above take precedence, you would write the following Rego.

ratelimit = 4 {
    input.name = "alice"
} else = 5 {
    input.owner = "bob"
}

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