Add sshchat dependencies in vendor

vendor/github.com/shazow/ssh-chat/sshd/auth.go

@@ -0,0 +1,72 @@
+package sshd
+
+import (
+	"crypto/sha256"
+	"encoding/base64"
+	"errors"
+	"net"
+
+	"golang.org/x/crypto/ssh"
+)
+
+// Auth is used to authenticate connections based on public keys.
+type Auth interface {
+	// Whether to allow connections without a public key.
+	AllowAnonymous() bool
+	// Given address and public key, return if the connection should be permitted.
+	Check(net.Addr, ssh.PublicKey) (bool, error)
+}
+
+// MakeAuth makes an ssh.ServerConfig which performs authentication against an Auth implementation.
+func MakeAuth(auth Auth) *ssh.ServerConfig {
+	config := ssh.ServerConfig{
+		NoClientAuth: false,
+		// Auth-related things should be constant-time to avoid timing attacks.
+		PublicKeyCallback: func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
+			ok, err := auth.Check(conn.RemoteAddr(), key)
+			if !ok {
+				return nil, err
+			}
+			perm := &ssh.Permissions{Extensions: map[string]string{
+				"pubkey": string(key.Marshal()),
+			}}
+			return perm, nil
+		},
+		KeyboardInteractiveCallback: func(conn ssh.ConnMetadata, challenge ssh.KeyboardInteractiveChallenge) (*ssh.Permissions, error) {
+			if !auth.AllowAnonymous() {
+				return nil, errors.New("public key authentication required")
+			}
+			_, err := auth.Check(conn.RemoteAddr(), nil)
+			return nil, err
+		},
+	}
+
+	return &config
+}
+
+// MakeNoAuth makes a simple ssh.ServerConfig which allows all connections.
+// Primarily used for testing.
+func MakeNoAuth() *ssh.ServerConfig {
+	config := ssh.ServerConfig{
+		NoClientAuth: false,
+		// Auth-related things should be constant-time to avoid timing attacks.
+		PublicKeyCallback: func(conn ssh.ConnMetadata, key ssh.PublicKey) (*ssh.Permissions, error) {
+			perm := &ssh.Permissions{Extensions: map[string]string{
+				"pubkey": string(key.Marshal()),
+			}}
+			return perm, nil
+		},
+		KeyboardInteractiveCallback: func(conn ssh.ConnMetadata, challenge ssh.KeyboardInteractiveChallenge) (*ssh.Permissions, error) {
+			return nil, nil
+		},
+	}
+
+	return &config
+}
+
+// Fingerprint performs a SHA256 BASE64 fingerprint of the PublicKey, similar to OpenSSH.
+// See: https://anongit.mindrot.org/openssh.git/commit/?id=56d1c83cdd1ac
+func Fingerprint(k ssh.PublicKey) string {
+	hash := sha256.Sum256(k.Marshal())
+	return "SHA256:" + base64.StdEncoding.EncodeToString(hash[:])
+}