smallstep-certificates/api/ssh.go

package api

import (
	"context"
	"encoding/base64"
	"encoding/json"
	"net/http"

	"github.com/pkg/errors"
	"github.com/smallstep/certificates/authority/provisioner"
	"golang.org/x/crypto/ssh"
)

// SSHAuthority is the interface implemented by a SSH CA authority.
type SSHAuthority interface {
	SignSSH(key ssh.PublicKey, opts provisioner.SSHOptions, signOpts ...provisioner.SignOption) (*ssh.Certificate, error)
	SignSSHAddUser(key ssh.PublicKey, cert *ssh.Certificate) (*ssh.Certificate, error)
}

// SignSSHRequest is the request body of an SSH certificate request.
type SignSSHRequest struct {
	PublicKey        []byte       `json:"publicKey"` //base64 encoded
	OTT              string       `json:"ott"`
	CertType         string       `json:"certType,omitempty"`
	Principals       []string     `json:"principals,omitempty"`
	ValidAfter       TimeDuration `json:"validAfter,omitempty"`
	ValidBefore      TimeDuration `json:"validBefore,omitempty"`
	AddUserPublicKey []byte       `json:"addUserPublicKey,omitempty"`
}

// SignSSHResponse is the response object that returns the SSH certificate.
type SignSSHResponse struct {
	Certificate        SSHCertificate  `json:"crt"`
	AddUserCertificate *SSHCertificate `json:"addUserCrt,omitempty"`
}

// SSHCertificate represents the response SSH certificate.
type SSHCertificate struct {
	*ssh.Certificate `json:"omitempty"`
}

// MarshalJSON implements the json.Marshaler interface. Returns a quoted,
// base64 encoded, openssh wire format version of the certificate.
func (c SSHCertificate) MarshalJSON() ([]byte, error) {
	if c.Certificate == nil {
		return []byte("null"), nil
	}
	s := base64.StdEncoding.EncodeToString(c.Certificate.Marshal())
	return []byte(`"` + s + `"`), nil
}

// UnmarshalJSON implements the json.Unmarshaler interface. The certificate is
// expected to be a quoted, base64 encoded, openssh wire formatted block of bytes.
func (c *SSHCertificate) UnmarshalJSON(data []byte) error {
	var s string
	if err := json.Unmarshal(data, &s); err != nil {
		return errors.Wrap(err, "error decoding certificate")
	}
	if s == "" {
		c.Certificate = nil
		return nil
	}
	certData, err := base64.StdEncoding.DecodeString(s)
	if err != nil {
		return errors.Wrap(err, "error decoding ssh certificate")
	}
	pub, err := ssh.ParsePublicKey(certData)
	if err != nil {
		return errors.Wrap(err, "error parsing ssh certificate")
	}
	cert, ok := pub.(*ssh.Certificate)
	if !ok {
		return errors.Errorf("error decoding ssh certificate: %T is not an *ssh.Certificate", pub)
	}
	c.Certificate = cert
	return nil
}

// Validate validates the SignSSHRequest.
func (s *SignSSHRequest) Validate() error {
	switch {
	case s.CertType != "" && s.CertType != provisioner.SSHUserCert && s.CertType != provisioner.SSHHostCert:
		return errors.Errorf("unknown certType %s", s.CertType)
	case len(s.PublicKey) == 0:
		return errors.New("missing or empty publicKey")
	case len(s.OTT) == 0:
		return errors.New("missing or empty ott")
	default:
		return nil
	}
}

// SignSSH is an HTTP handler that reads an SignSSHRequest with a one-time-token
// (ott) from the body and creates a new SSH certificate with the information in
// the request.
func (h *caHandler) SignSSH(w http.ResponseWriter, r *http.Request) {
	var body SignSSHRequest
	if err := ReadJSON(r.Body, &body); err != nil {
		WriteError(w, BadRequest(errors.Wrap(err, "error reading request body")))
		return
	}

	logOtt(w, body.OTT)
	if err := body.Validate(); err != nil {
		WriteError(w, BadRequest(err))
		return
	}

	publicKey, err := ssh.ParsePublicKey(body.PublicKey)
	if err != nil {
		WriteError(w, BadRequest(errors.Wrap(err, "error parsing publicKey")))
		return
	}

	var addUserPublicKey ssh.PublicKey
	if body.AddUserPublicKey != nil {
		addUserPublicKey, err = ssh.ParsePublicKey(body.AddUserPublicKey)
		if err != nil {
			WriteError(w, BadRequest(errors.Wrap(err, "error parsing addUserPublicKey")))
			return
		}
	}

	opts := provisioner.SSHOptions{
		CertType:    body.CertType,
		Principals:  body.Principals,
		ValidBefore: body.ValidBefore,
		ValidAfter:  body.ValidAfter,
	}

	ctx := provisioner.NewContextWithMethod(context.Background(), provisioner.SignSSHMethod)
	signOpts, err := h.Authority.Authorize(ctx, body.OTT)
	if err != nil {
		WriteError(w, Unauthorized(err))
		return
	}

	cert, err := h.Authority.SignSSH(publicKey, opts, signOpts...)
	if err != nil {
		WriteError(w, Forbidden(err))
		return
	}

	var addUserCertificate *SSHCertificate
	if addUserPublicKey != nil && cert.CertType == ssh.UserCert && len(cert.ValidPrincipals) == 1 {
		addUserCert, err := h.Authority.SignSSHAddUser(addUserPublicKey, cert)
		if err != nil {
			WriteError(w, Forbidden(err))
			return
		}
		addUserCertificate = &SSHCertificate{addUserCert}
	}

	w.WriteHeader(http.StatusCreated)
	JSON(w, &SignSSHResponse{
		Certificate:        SSHCertificate{cert},
		AddUserCertificate: addUserCertificate,
	})
}