Implement command-based echo app and HTTP handler

keystore.go

@@ -0,0 +1,17 @@
+package ussher
+
+import "golang.org/x/crypto/ssh"
+
+type Keystore interface {
+	CheckPublicKey(user string, key ssh.PublicKey) (*ssh.Permissions, error)
+}
+
+func AcceptAllKeys() *allKeyAcceptor {
+	return &allKeyAcceptor{}
+}
+
+type allKeyAcceptor struct{}
+
+func (all *allKeyAcceptor) CheckPublicKey(user string, key ssh.PublicKey) (*ssh.Permissions, error) {
+	return nil, nil
+}