Timeout Caveat Support

.gitignore

@@ -13,3 +13,6 @@
 
 /aperture
 cmd/aperture/aperture
+
+# misc
+.vscode

aperture.go

@@ -662,6 +662,7 @@ func createProxy(cfg *Config, challenger *LndChallenger,
 		Challenger:     challenger,
 		Secrets:        newSecretStore(etcdClient),
 		ServiceLimiter: newStaticServiceLimiter(cfg.Services),
+		Now:            time.Now,
 	})
 	authenticator := auth.NewLsatAuthenticator(minter, challenger)
 

lsat/satisfier.go

@@ -2,7 +2,9 @@ package lsat
 
 import (
 	"fmt"
+	"strconv"
 	"strings"
+	"time"
 )
 
 // Satisfier provides a generic interface to satisfy a caveat based on its
@@ -79,7 +81,9 @@ func NewServicesSatisfier(targetService string) Satisfier {
 
 // NewCapabilitiesSatisfier implements a satisfier to determine whether the
 // target capability for a service is authorized for a given LSAT.
-func NewCapabilitiesSatisfier(service string, targetCapability string) Satisfier {
+func NewCapabilitiesSatisfier(service string,
+	targetCapability string) Satisfier {
+
 	return Satisfier{
 		Condition: service + CondCapabilitiesSuffix,
 		SatisfyPrevious: func(prev, cur Caveat) error {
@@ -115,3 +119,62 @@ func NewCapabilitiesSatisfier(service string, targetCapability string) Satisfier
 		},
 	}
 }
+
+// NewTimeoutSatisfier checks if an LSAT is expired or not. The Satisfier takes
+// a service name to set as the condition prefix and currentTimestamp to
+// compare against the expiration(s) in the caveats. The expiration time is
+// retrieved from the caveat values themselves. The satisfier will also make
+// sure that each subsequent caveat of the same condition only has increasingly
+// strict expirations.
+func NewTimeoutSatisfier(service string, now func() time.Time) Satisfier {
+	return Satisfier{
+		Condition: service + CondTimeoutSuffix,
+		SatisfyPrevious: func(prev, cur Caveat) error {
+			prevValue, err := strconv.ParseInt(prev.Value, 10, 64)
+			if err != nil {
+				return fmt.Errorf("error parsing previous "+
+					"caveat value: %w", err)
+			}
+
+			currValue, err := strconv.ParseInt(cur.Value, 10, 64)
+			if err != nil {
+				return fmt.Errorf("error parsing caveat "+
+					"value: %w", err)
+			}
+
+			prevTime := time.Unix(prevValue, 0)
+			currTime := time.Unix(currValue, 0)
+
+			// Satisfier should fail if a previous timestamp in the
+			// list is earlier than ones after it b/c that means
+			// they are getting more permissive.
+			if prevTime.Before(currTime) {
+				return fmt.Errorf("%s caveat violates "+
+					"increasing restrictiveness",
+					service+CondTimeoutSuffix)
+			}
+
+			return nil
+		},
+		SatisfyFinal: func(c Caveat) error {
+			expirationTimestamp, err := strconv.ParseInt(
+				c.Value, 10, 64,
+			)
+			if err != nil {
+				return fmt.Errorf("caveat value not a valid "+
+					"integer: %v", err)
+			}
+
+			expirationTime := time.Unix(expirationTimestamp, 0)
+
+			// Make sure that the final relevant caveat is not
+			// passed the current date/time.
+			if now().Before(expirationTime) {
+				return nil
+			}
+
+			return fmt.Errorf("not authorized to access " +
+				"service. LSAT has expired")
+		},
+	}
+}

lsat/satisfier_test.go

@@ -0,0 +1,87 @@
+package lsat
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+// TestTimeoutSatisfier tests that the Timeout Satisfier implementation behaves
+// as expected and correctly accepts or rejects calls based on if the
+// timeout has been reached or not.
+func TestTimeoutSatisfier(t *testing.T) {
+	t.Parallel()
+
+	now := int64(0)
+
+	var tests = []struct {
+		name           string
+		timeouts       []int64
+		expectFinalErr bool
+		expectPrevErr  bool
+	}{
+		{
+			name:     "current time is before expiration",
+			timeouts: []int64{now + 1000},
+		},
+		{
+			name: "time passed is greater than " +
+				"expiration",
+			timeouts:       []int64{now - 1000},
+			expectFinalErr: true,
+		},
+		{
+			name: "successive caveats are increasingly " +
+				"restrictive and not yet expired",
+			timeouts: []int64{now + 1000, now + 500},
+		},
+		{
+			name: "latter caveat is less restrictive " +
+				"then previous",
+			timeouts:      []int64{now + 500, now + 1000},
+			expectPrevErr: true,
+		},
+	}
+
+	var (
+		service   = "restricted"
+		condition = service + CondTimeoutSuffix
+		satisfier = NewTimeoutSatisfier(service, func() time.Time {
+			return time.Unix(now, 0)
+		})
+	)
+
+	for _, test := range tests {
+		test := test
+		t.Run(test.name, func(t *testing.T) {
+			var prev *Caveat
+			for _, timeout := range test.timeouts {
+				caveat := NewCaveat(
+					condition, fmt.Sprintf("%d", timeout),
+				)
+
+				if prev != nil {
+					err := satisfier.SatisfyPrevious(
+						*prev, caveat,
+					)
+					if test.expectPrevErr {
+						require.Error(t, err)
+					} else {
+						require.NoError(t, err)
+					}
+				}
+
+				err := satisfier.SatisfyFinal(caveat)
+				if test.expectFinalErr {
+					require.Error(t, err)
+				} else {
+					require.NoError(t, err)
+				}
+
+				prev = &caveat
+			}
+		})
+	}
+}

lsat/service.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"time"
 )
 
 const (
@@ -15,6 +16,10 @@ const (
 	// capabilities caveat. For example, the condition of a capabilities
 	// caveat for a service named `loop` would be `loop_capabilities`.
 	CondCapabilitiesSuffix = "_capabilities"
+
+	// CondTimeoutSuffix is the condition suffix used for a service's
+	// timeout caveat.
+	CondTimeoutSuffix = "_valid_until"
 )
 
 var (
@@ -129,3 +134,19 @@ func NewCapabilitiesCaveat(serviceName string, capabilities string) Caveat {
 		Value:     capabilities,
 	}
 }
+
+// NewTimeoutCaveat creates a new caveat that will result in a macaroon being
+// valid for numSeconds after the current time.
+func NewTimeoutCaveat(serviceName string, numSeconds int64,
+	now func() time.Time) Caveat {
+
+	var (
+		macaroonTimeout = time.Duration(numSeconds) * time.Second
+		requestTimeout  = now().Add(macaroonTimeout)
+	)
+
+	return Caveat{
+		Condition: serviceName + CondTimeoutSuffix,
+		Value:     strconv.FormatInt(requestTimeout.Unix(), 10),
+	}
+}

mint/mint.go

@@ -7,6 +7,7 @@ import (
 	"crypto/sha256"
 	"errors"
 	"fmt"
+	"time"
 
 	"github.com/lightninglabs/aperture/lsat"
 	"github.com/lightningnetwork/lnd/lntypes"
@@ -60,6 +61,10 @@ type ServiceLimiter interface {
 	// enforces additional constraints on a particular service/service
 	// capability.
 	ServiceConstraints(context.Context, ...lsat.Service) ([]lsat.Caveat, error)
+
+	// ServiceTimeouts returns the timeout caveat for each service. This
+	// will determine if and when service access can expire.
+	ServiceTimeouts(context.Context, ...lsat.Service) ([]lsat.Caveat, error)
 }
 
 // Config packages all of the required dependencies to instantiate a new LSAT
@@ -76,6 +81,9 @@ type Config struct {
 	// ServiceLimiter provides us with how we should limit a new LSAT based
 	// on its target services.
 	ServiceLimiter ServiceLimiter
+
+	// Now returns the current time.
+	Now func() time.Time
 }
 
 // Mint is an entity that is able to mint and verify LSATs for a set of
@@ -210,10 +218,15 @@ func (m *Mint) caveatsForServices(ctx context.Context,
 	if err != nil {
 		return nil, err
 	}
+	timeouts, err := m.cfg.ServiceLimiter.ServiceTimeouts(ctx, services...)
+	if err != nil {
+		return nil, err
+	}
 
 	caveats := []lsat.Caveat{servicesCaveat}
 	caveats = append(caveats, capabilities...)
 	caveats = append(caveats, constraints...)
+	caveats = append(caveats, timeouts...)
 	return caveats, nil
 }
 
@@ -269,6 +282,8 @@ func (m *Mint) VerifyLSAT(ctx context.Context, params *VerificationParams) error
 		caveats = append(caveats, caveat)
 	}
 	return lsat.VerifyCaveats(
-		caveats, lsat.NewServicesSatisfier(params.TargetService),
+		caveats,
+		lsat.NewServicesSatisfier(params.TargetService),
+		lsat.NewTimeoutSatisfier(params.TargetService, m.cfg.Now),
 	)
 }