Pomerium Policy Language (#2202)

* policy: add parser and generator for Pomerium Policy Language

* add criteria

* add additional criteria

pkg/policy/criteria/reject.go

@@ -0,0 +1,35 @@
+package criteria
+
+import (
+	"github.com/open-policy-agent/opa/ast"
+
+	"github.com/pomerium/pomerium/pkg/policy/parser"
+)
+
+var rejectBody = ast.Body{
+	ast.MustParseExpr(`v := false`),
+}
+
+type rejectMatcher struct {
+	g *Generator
+}
+
+func (rejectMatcher) Names() []string {
+	return []string{"reject"}
+}
+
+func (m rejectMatcher) GenerateRule(_ string, _ parser.Value) (*ast.Rule, []*ast.Rule, error) {
+	rule := m.g.NewRule("reject")
+	rule.Head.Value = ast.VarTerm("v")
+	rule.Body = rejectBody
+	return rule, nil, nil
+}
+
+// Reject returns a Criterion which always returns false.
+func Reject(generator *Generator) Criterion {
+	return rejectMatcher{g: generator}
+}
+
+func init() {
+	Register(Reject)
+}