Update go dependencies

vendor/golang.org/x/crypto/ssh/server.go

@@ -95,6 +95,10 @@ type ServerConfig struct {
 	// Note that RFC 4253 section 4.2 requires that this string start with
 	// "SSH-2.0-".
 	ServerVersion string
+
+	// BannerCallback, if present, is called and the return string is sent to
+	// the client after key exchange completed but before authentication.
+	BannerCallback func(conn ConnMetadata) string
 }
 
 // AddHostKey adds a private key as a host key. If an existing host
@@ -162,6 +166,9 @@ type ServerConn struct {
 // unsuccessful, it closes the connection and returns an error.  The
 // Request and NewChannel channels must be serviced, or the connection
 // will hang.
+//
+// The returned error may be of type *ServerAuthError for
+// authentication errors.
 func NewServerConn(c net.Conn, config *ServerConfig) (*ServerConn, <-chan NewChannel, <-chan *Request, error) {
 	fullConf := *config
 	fullConf.SetDefaults()
@@ -252,7 +259,7 @@ func (s *connection) serverHandshake(config *ServerConfig) (*Permissions, error)
 func isAcceptableAlgo(algo string) bool {
 	switch algo {
 	case KeyAlgoRSA, KeyAlgoDSA, KeyAlgoECDSA256, KeyAlgoECDSA384, KeyAlgoECDSA521, KeyAlgoED25519,
-		CertAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01, CertAlgoECDSA384v01, CertAlgoECDSA521v01:
+		CertAlgoRSAv01, CertAlgoDSAv01, CertAlgoECDSA256v01, CertAlgoECDSA384v01, CertAlgoECDSA521v01, CertAlgoED25519v01:
 		return true
 	}
 	return false
@@ -288,12 +295,13 @@ func checkSourceAddress(addr net.Addr, sourceAddrs string) error {
 	return fmt.Errorf("ssh: remote address %v is not allowed because of source-address restriction", addr)
 }
 
-// ServerAuthError implements the error interface. It appends any authentication
-// errors that may occur, and is returned if all of the authentication methods
-// provided by the user failed to authenticate.
+// ServerAuthError represents server authentication errors and is
+// sometimes returned by NewServerConn. It appends any authentication
+// errors that may occur, and is returned if all of the authentication
+// methods provided by the user failed to authenticate.
 type ServerAuthError struct {
 	// Errors contains authentication errors returned by the authentication
-	// callback methods.
+	// callback methods. The first entry is typically ErrNoAuth.
 	Errors []error
 }
 
@@ -305,6 +313,13 @@ func (l ServerAuthError) Error() string {
 	return "[" + strings.Join(errs, ", ") + "]"
 }
 
+// ErrNoAuth is the error value returned if no
+// authentication method has been passed yet. This happens as a normal
+// part of the authentication loop, since the client first tries
+// 'none' authentication to discover available methods.
+// It is returned in ServerAuthError.Errors from NewServerConn.
+var ErrNoAuth = errors.New("ssh: no auth passed yet")
+
 func (s *connection) serverAuthenticate(config *ServerConfig) (*Permissions, error) {
 	sessionID := s.transport.getSessionID()
 	var cache pubKeyCache
@@ -312,6 +327,7 @@ func (s *connection) serverAuthenticate(config *ServerConfig) (*Permissions, err
 
 	authFailures := 0
 	var authErrs []error
+	var displayedBanner bool
 
 userAuthLoop:
 	for {
@@ -343,8 +359,22 @@ userAuthLoop:
 		}
 
 		s.user = userAuthReq.User
+
+		if !displayedBanner && config.BannerCallback != nil {
+			displayedBanner = true
+			msg := config.BannerCallback(s)
+			if msg != "" {
+				bannerMsg := &userAuthBannerMsg{
+					Message: msg,
+				}
+				if err := s.transport.writePacket(Marshal(bannerMsg)); err != nil {
+					return nil, err
+				}
+			}
+		}
+
 		perms = nil
-		authErr := errors.New("no auth passed yet")
+		authErr := ErrNoAuth
 
 		switch userAuthReq.Method {
 		case "none":