add vendoring

vendor/github.com/mikesmitty/edkey/LICENSE

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+MIT License
+
+Copyright (c) 2017 Michael Smith
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

vendor/github.com/mikesmitty/edkey/README.md

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+# edkey
+edkey allows you to marshal/write ED25519 private keys in the OpenSSH private key format
+
+## Example
+```go
+package main
+
+import (
+	"crypto/rand"
+	"encoding/pem"
+	"io/ioutil"
+	"github.com/mikesmitty/edkey"
+	"golang.org/x/crypto/ed25519"
+	"golang.org/x/crypto/ssh"
+)
+
+func main() {
+	// Generate a new private/public keypair for OpenSSH
+	pubKey, privKey, _ := ed25519.GenerateKey(rand.Reader)
+	publicKey, _ := ssh.NewPublicKey(pubKey)
+
+	pemKey := &pem.Block{
+		Type:  "OPENSSH PRIVATE KEY",
+		Bytes: edkey.MarshalED25519PrivateKey(privKey),
+	}
+	privateKey := pem.EncodeToMemory(pemKey)
+	authorizedKey := ssh.MarshalAuthorizedKey(publicKey)
+
+	_ = ioutil.WriteFile("id_ed25519", privateKey, 0600)
+	_ = ioutil.WriteFile("id_ed25519.pub", authorizedKey, 0644)
+}
+```

vendor/github.com/mikesmitty/edkey/edkey.go

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+package edkey
+
+import (
+	"math/rand"
+
+	"golang.org/x/crypto/ed25519"
+	"golang.org/x/crypto/ssh"
+)
+
+/* Writes ed25519 private keys into the new OpenSSH private key format.
+I have no idea why this isn't implemented anywhere yet, you can do seemingly
+everything except write it to disk in the OpenSSH private key format. */
+func MarshalED25519PrivateKey(key ed25519.PrivateKey) []byte {
+	// Add our key header (followed by a null byte)
+	magic := append([]byte("openssh-key-v1"), 0)
+
+	var w struct {
+		CipherName   string
+		KdfName      string
+		KdfOpts      string
+		NumKeys      uint32
+		PubKey       []byte
+		PrivKeyBlock []byte
+	}
+
+	// Fill out the private key fields
+	pk1 := struct {
+		Check1  uint32
+		Check2  uint32
+		Keytype string
+		Pub     []byte
+		Priv    []byte
+		Comment string
+		Pad     []byte `ssh:"rest"`
+	}{}
+
+	// Set our check ints
+	ci := rand.Uint32()
+	pk1.Check1 = ci
+	pk1.Check2 = ci
+
+	// Set our key type
+	pk1.Keytype = ssh.KeyAlgoED25519
+
+	// Add the pubkey to the optionally-encrypted block
+	pk, ok := key.Public().(ed25519.PublicKey)
+	if !ok {
+		//fmt.Fprintln(os.Stderr, "ed25519.PublicKey type assertion failed on an ed25519 public key. This should never ever happen.")
+		return nil
+	}
+	pubKey := []byte(pk)
+	pk1.Pub = pubKey
+
+	// Add our private key
+	pk1.Priv = []byte(key)
+
+	// Might be useful to put something in here at some point
+	pk1.Comment = ""
+
+	// Add some padding to match the encryption block size within PrivKeyBlock (without Pad field)
+	// 8 doesn't match the documentation, but that's what ssh-keygen uses for unencrypted keys. *shrug*
+	bs := 8
+	blockLen := len(ssh.Marshal(pk1))
+	padLen := (bs - (blockLen % bs)) % bs
+	pk1.Pad = make([]byte, padLen)
+
+	// Padding is a sequence of bytes like: 1, 2, 3...
+	for i := 0; i < padLen; i++ {
+		pk1.Pad[i] = byte(i + 1)
+	}
+
+	// Generate the pubkey prefix "\0\0\0\nssh-ed25519\0\0\0 "
+	prefix := []byte{0x0, 0x0, 0x0, 0x0b}
+	prefix = append(prefix, []byte(ssh.KeyAlgoED25519)...)
+	prefix = append(prefix, []byte{0x0, 0x0, 0x0, 0x20}...)
+
+	// Only going to support unencrypted keys for now
+	w.CipherName = "none"
+	w.KdfName = "none"
+	w.KdfOpts = ""
+	w.NumKeys = 1
+	w.PubKey = append(prefix, pubKey...)
+	w.PrivKeyBlock = ssh.Marshal(pk1)
+
+	magic = append(magic, ssh.Marshal(w)...)
+
+	return magic
+}