Add leases api

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

leases/context.go

@@ -0,0 +1,24 @@
+package leases
+
+import "context"
+
+type leaseKey struct{}
+
+// WithLease sets a given lease on the context
+func WithLease(ctx context.Context, lid string) context.Context {
+	ctx = context.WithValue(ctx, leaseKey{}, lid)
+
+	// also store on the grpc headers so it gets picked up by any clients that
+	// are using this.
+	return withGRPCLeaseHeader(ctx, lid)
+}
+
+// Lease returns the lease from the context.
+func Lease(ctx context.Context) (string, bool) {
+	lid, ok := ctx.Value(leaseKey{}).(string)
+	if !ok {
+		return fromGRPCHeader(ctx)
+	}
+
+	return lid, ok
+}