/*
Copyright 2015 Gravitational, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

// Package auth implements certificate signing authority and access control server
// Authority server is composed of several parts:
//
// * Authority server itself that implements signing and acl logic
// * HTTP server wrapper for authority server
// * HTTP client wrapper
//
package auth

import (
	"fmt"
	"net/url"
	"os"
	"sync"
	"time"

	"github.com/gravitational/teleport"
	"github.com/gravitational/teleport/lib/backend"
	"github.com/gravitational/teleport/lib/defaults"
	"github.com/gravitational/teleport/lib/services"
	"github.com/gravitational/teleport/lib/services/local"
	"github.com/gravitational/teleport/lib/utils"

	log "github.com/Sirupsen/logrus"
	"github.com/coreos/go-oidc/oauth2"
	"github.com/coreos/go-oidc/oidc"
	"github.com/gravitational/trace"
	"github.com/jonboulle/clockwork"
)

// Authority implements minimal key-management facility for generating OpenSSH
//compatible public/private key pairs and OpenSSH certificates
type Authority interface {
	// GenerateKeyPair generates new keypair
	GenerateKeyPair(passphrase string) (privKey []byte, pubKey []byte, err error)

	// GetNewKeyPairFromPool returns new keypair from pre-generated in memory pool
	GetNewKeyPairFromPool() (privKey []byte, pubKey []byte, err error)

	// GenerateHostCert generates host certificate, it takes pkey as a signing
	// private key (host certificate authority)
	GenerateHostCert(pkey, key []byte, hostID, authDomain string, roles teleport.Roles, ttl time.Duration) ([]byte, error)

	// GenerateUserCert generates user certificate, it takes pkey as a signing
	// private key (user certificate authority)
	GenerateUserCert(pkey, key []byte, teleportUsername string, allowedLogins []string, ttl time.Duration) ([]byte, error)
}

// Session is a web session context, stores temporary key-value pair and session id
type Session struct {
	// ID is a session ID
	ID string `json:"id"`
	// Username is a user this session belongs to
	Username string `json:"username"`
	// ExpiresAt is an optional expiry time, if set
	// that means this web session and all derived web sessions
	// can not continue after this time, used in OIDC use case
	// when expiry is set by external identity provider, so user
	// has to relogin (or later on we'd need to refresh the token)
	ExpiresAt time.Time `json:"expires_at"`
	// WS is a private keypair used for signing requests
	WS services.WebSession `json:"web"`
}

// AuthServerOption allows setting options as functional arguments to AuthServer
type AuthServerOption func(*AuthServer)

// NewAuthServer creates and configures a new AuthServer instance
func NewAuthServer(cfg *InitConfig, opts ...AuthServerOption) *AuthServer {
	if cfg.Trust == nil {
		cfg.Trust = local.NewCAService(cfg.Backend)
	}
	if cfg.Lock == nil {
		cfg.Lock = local.NewLockService(cfg.Backend)
	}
	if cfg.Presence == nil {
		cfg.Presence = local.NewPresenceService(cfg.Backend)
	}
	if cfg.Provisioner == nil {
		cfg.Provisioner = local.NewProvisioningService(cfg.Backend)
	}
	if cfg.Identity == nil {
		cfg.Identity = local.NewIdentityService(cfg.Backend)
	}
	as := AuthServer{
		bk:              cfg.Backend,
		Authority:       cfg.Authority,
		Trust:           cfg.Trust,
		Lock:            cfg.Lock,
		Presence:        cfg.Presence,
		Provisioner:     cfg.Provisioner,
		Identity:        cfg.Identity,
		DomainName:      cfg.DomainName,
		AuthServiceName: cfg.AuthServiceName,
		oidcClients:     make(map[string]*oidc.Client),
		StaticTokens:    cfg.StaticTokens,
	}
	for _, o := range opts {
		o(&as)
	}
	if as.clock == nil {
		as.clock = clockwork.NewRealClock()
	}
	return &as
}

// AuthServer keeps the cluster together. It acts as a certificate authority (CA) for
// a cluster and:
//   - generates the keypair for the node it's running on
//	 - invites other SSH nodes to a cluster, by issuing invite tokens
//	 - adds other SSH nodes to a cluster, by checking their token and signing their keys
//   - same for users and their sessions
//   - checks public keys to see if they're signed by it (can be trusted or not)
type AuthServer struct {
	lock        sync.Mutex
	oidcClients map[string]*oidc.Client
	clock       clockwork.Clock
	bk          backend.Backend
	Authority

	// DomainName stores the FQDN of the signing CA (its certificate will have this
	// name embedded). It is usually set to the GUID of the host the Auth service runs on
	DomainName string

	// AuthServiceName is a human-readable name of this CA. If several Auth services are running
	// (managing multiple teleport clusters) this field is used to tell them apart in UIs
	// It usually defaults to the hostname of the machine the Auth service runs on.
	AuthServiceName string

	// StaticTokens are pre-defined host provisioning tokens supplied via config file for
	// environments where paranoid security is not needed
	StaticTokens []StaticToken

	services.Trust
	services.Lock
	services.Presence
	services.Provisioner
	services.Identity
}

func (a *AuthServer) Close() error {
	if a.bk != nil {
		return trace.Wrap(a.bk.Close())
	}
	return nil
}

// GetLocalDomain returns domain name that identifies this authority server
func (a *AuthServer) GetLocalDomain() (string, error) {
	return a.DomainName, nil
}

// GenerateHostCert generates host certificate, it takes pkey as a signing
// private key (host certificate authority)
func (s *AuthServer) GenerateHostCert(key []byte, hostID, authDomain string, roles teleport.Roles, ttl time.Duration) ([]byte, error) {
	ca, err := s.Trust.GetCertAuthority(services.CertAuthID{
		Type:       services.HostCA,
		DomainName: s.DomainName,
	}, true)
	if err != nil {
		return nil, trace.Errorf("failed to load host CA for '%s': %v", s.DomainName, err)
	}
	privateKey, err := ca.FirstSigningKey()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return s.Authority.GenerateHostCert(privateKey, key, hostID, authDomain, roles, ttl)
}

// GenerateUserCert generates user certificate, it takes pkey as a signing
// private key (user certificate authority)
func (s *AuthServer) GenerateUserCert(
	key []byte, username string, ttl time.Duration) ([]byte, error) {

	ca, err := s.Trust.GetCertAuthority(services.CertAuthID{
		Type:       services.UserCA,
		DomainName: s.DomainName,
	}, true)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	privateKey, err := ca.FirstSigningKey()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	user, err := s.GetUser(username)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return s.Authority.GenerateUserCert(privateKey, key, username, user.GetAllowedLogins(), ttl)
}

func (s *AuthServer) SignIn(user string, password []byte) (*Session, error) {
	if err := s.CheckPasswordWOToken(user, password); err != nil {
		return nil, trace.Wrap(err)
	}
	sess, err := s.NewWebSession(user)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	if err := s.UpsertWebSession(user, sess, WebSessionTTL); err != nil {
		return nil, trace.Wrap(err)
	}
	sess.WS.Priv = nil
	return sess, nil
}

// ExtendWebSession creates a new web session for a user based on a valid previous sessionID,
// method is used to renew the web session for a user
func (s *AuthServer) ExtendWebSession(user string, prevSessionID string) (*Session, error) {
	prevSession, err := s.GetWebSession(user, prevSessionID)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	// consider absolute expiry time that may be set for this session
	// by some external identity serivce, so we can not renew this session
	// any more without extra logic for renewal with external OIDC provider
	expiresAt := prevSession.ExpiresAt
	if !expiresAt.IsZero() && expiresAt.Before(s.clock.Now().UTC()) {
		return nil, trace.NotFound("web session has expired")
	}

	sess, err := s.NewWebSession(user)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	sessionTTL := minTTL(toTTL(s.clock, expiresAt), WebSessionTTL)
	sess.ExpiresAt = expiresAt
	if err := s.UpsertWebSession(user, sess, sessionTTL); err != nil {
		return nil, trace.Wrap(err)
	}
	sess.WS.Priv = nil
	return sess, nil
}

// CreateWebSession creates a new web session for user without any
// checks, is used by admins
func (s *AuthServer) CreateWebSession(user string) (*Session, error) {
	sess, err := s.NewWebSession(user)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	if err := s.UpsertWebSession(user, sess, WebSessionTTL); err != nil {
		return nil, trace.Wrap(err)
	}
	sess.WS.Priv = nil
	return sess, nil
}

func (s *AuthServer) GenerateToken(roles teleport.Roles, ttl time.Duration) (string, error) {
	for _, role := range roles {
		if err := role.Check(); err != nil {
			return "", trace.Wrap(err)
		}
	}
	token, err := utils.CryptoRandomHex(TokenLenBytes)
	if err != nil {
		return "", trace.Wrap(err)
	}
	if err := s.Provisioner.UpsertToken(token, roles, ttl); err != nil {
		return "", err
	}
	return token, nil
}

func (s *AuthServer) ValidateToken(token string) (roles teleport.Roles, e error) {
	tok, err := s.Provisioner.GetToken(token)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return tok.Roles, nil
}

// GenerateServerKeys generates private key and certificate signed
// by the host certificate authority, listing the role of this server
func (s *AuthServer) GenerateServerKeys(hostID string, roles teleport.Roles) (*PackedKeys, error) {
	k, pub, err := s.GenerateKeyPair("")
	if err != nil {
		return nil, trace.Wrap(err)
	}
	// we always append authority's domain to resulting node name,
	// that's how we make sure that nodes are uniquely identified/found
	// in cases when we have multiple environments/organizations
	fqdn := fmt.Sprintf("%s.%s", hostID, s.DomainName)
	c, err := s.GenerateHostCert(pub, fqdn, s.DomainName, roles, 0)
	if err != nil {
		log.Warningf("[AUTH] Node `%v` cannot join: cert generation error. %v", hostID, err)
		return nil, trace.Wrap(err)
	}

	return &PackedKeys{
		Key:  k,
		Cert: c,
	}, nil
}

// RegisterUsingToken adds a new node to the Teleport cluster using previously issued token.
// A node must also request a specific role (and the role must match one of the roles
// the token was generated for).
//
// If a token was generated with a TTL, it gets enforced (can't register new nodes after TTL expires)
// If a token was generated with a TTL=0, it means it's a single-use token and it gets destroyed
// after a successful registration.
func (s *AuthServer) RegisterUsingToken(token, hostID string, role teleport.Role) (*PackedKeys, error) {
	log.Infof("[AUTH] Node `%v` is trying to join as %v", hostID, role)
	if hostID == "" {
		return nil, trace.BadParameter("HostID cannot be empty")
	}
	if err := role.Check(); err != nil {
		return nil, trace.Wrap(err)
	}
	// check against static tokens first:
	foundStaticToken := false
	for _, st := range s.StaticTokens {
		if st.Value == token {
			if st.Roles.Include(role) {
				foundStaticToken = true
				break
			}
		}
	}
	// look for the generated token in the token storage:
	if !foundStaticToken {
		tok, err := s.Provisioner.GetToken(token)
		if err != nil {
			log.Warningf("[AUTH] Node `%v` cannot join: token error. %v", hostID, err)
			return nil, trace.Wrap(err)
		}
		// check token's role:
		if !tok.Roles.Include(role) {
			return nil, trace.BadParameter("token.Role: role does not match")
		}
		// check token TTL:
		if tok.TTL > 0 {
			now := s.clock.Now().UTC()
			if tok.Created.Add(tok.TTL).Before(now) {
				err = s.DeleteToken(token)
				if err != nil {
					log.Error(err)
				}
				return nil, trace.Errorf("token expired")
			}
			// TTL==0? this is a single-use token: delete it
		} else {
			if err = s.DeleteToken(token); err != nil {
				log.Error(err)
			}
		}
	}

	keys, err := s.GenerateServerKeys(hostID, teleport.Roles{role})
	if err != nil {
		return nil, trace.Wrap(err)
	}
	utils.Consolef(os.Stdout, "[AUTH] Node `%v` joined the cluster", hostID)
	return keys, nil
}

func (s *AuthServer) RegisterNewAuthServer(token string) error {
	tok, err := s.Provisioner.GetToken(token)
	if err != nil {
		return trace.Wrap(err)
	}
	if !tok.Roles.Include(teleport.RoleAuth) {
		return trace.AccessDenied("role does not match")
	}
	if err := s.DeleteToken(token); err != nil {
		return trace.Wrap(err)
	}
	return nil
}

func (s *AuthServer) DeleteToken(token string) error {
	return s.Provisioner.DeleteToken(token)
}

func (s *AuthServer) NewWebSession(userName string) (*Session, error) {
	token, err := utils.CryptoRandomHex(WebSessionTokenLenBytes)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	bearerToken, err := utils.CryptoRandomHex(WebSessionTokenLenBytes)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	priv, pub, err := s.GetNewKeyPairFromPool()
	if err != nil {
		return nil, err
	}
	ca, err := s.Trust.GetCertAuthority(services.CertAuthID{
		Type:       services.UserCA,
		DomainName: s.DomainName,
	}, true)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	privateKey, err := ca.FirstSigningKey()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	user, err := s.GetUser(userName)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	cert, err := s.Authority.GenerateUserCert(privateKey, pub, user.GetName(), user.GetAllowedLogins(), WebSessionTTL)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	sess := &Session{
		ID:       token,
		Username: user.GetName(),
		WS: services.WebSession{
			Priv:        priv,
			Pub:         cert,
			Expires:     s.clock.Now().UTC().Add(WebSessionTTL),
			BearerToken: bearerToken,
		},
	}
	return sess, nil
}

func (s *AuthServer) UpsertWebSession(user string, sess *Session, ttl time.Duration) error {
	return s.Identity.UpsertWebSession(user, sess.ID, sess.WS, ttl)
}

func (s *AuthServer) GetWebSession(userName string, id string) (*Session, error) {
	ws, err := s.Identity.GetWebSession(userName, id)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	user, err := s.GetUser(userName)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return &Session{
		ID:       id,
		Username: user.GetName(),
		WS:       *ws,
	}, nil
}

func (s *AuthServer) GetWebSessionInfo(userName string, id string) (*Session, error) {
	sess, err := s.Identity.GetWebSession(userName, id)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	user, err := s.GetUser(userName)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	sess.Priv = nil
	return &Session{
		ID:       id,
		Username: user.GetName(),
		WS:       *sess,
	}, nil
}

func (s *AuthServer) DeleteWebSession(user string, id string) error {
	return trace.Wrap(s.Identity.DeleteWebSession(user, id))
}

func (s *AuthServer) getOIDCClient(conn *services.OIDCConnector) (*oidc.Client, error) {
	s.lock.Lock()
	defer s.lock.Unlock()

	client, ok := s.oidcClients[conn.ID]
	if ok {
		return client, nil
	}

	config := oidc.ClientConfig{
		RedirectURL: conn.RedirectURL,
		Credentials: oidc.ClientCredentials{
			ID:     conn.ClientID,
			Secret: conn.ClientSecret,
		},
		// open id notifies provider that we are using OIDC scopes
		Scope: []string{"openid", "email"},
	}

	client, err := oidc.NewClient(config)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	client.SyncProviderConfig(conn.IssuerURL)

	s.oidcClients[conn.ID] = client

	return client, nil
}

func (s *AuthServer) CreateOIDCAuthRequest(req services.OIDCAuthRequest) (*services.OIDCAuthRequest, error) {
	connector, err := s.Identity.GetOIDCConnector(req.ConnectorID, true)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	oidcClient, err := s.getOIDCClient(connector)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	token, err := utils.CryptoRandomHex(WebSessionTokenLenBytes)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	req.StateToken = token

	oauthClient, err := oidcClient.OAuthClient()
	if err != nil {
		return nil, trace.Wrap(err)
	}
	// online is OIDC online scope, "select_account" forces user to always select account
	redirectURL := oauthClient.AuthCodeURL(req.StateToken, "online", "select_account")
	req.RedirectURL = redirectURL

	err = s.Identity.CreateOIDCAuthRequest(req, defaults.OIDCAuthRequestTTL)
	if err != nil {
		return nil, trace.Wrap(err)
	}
	return &req, nil
}

// OIDCAuthResponse is returned when auth server validated callback parameters
// returned from OIDC provider
type OIDCAuthResponse struct {
	// Username is authenticated teleport username
	Username string `json:"username"`
	// Identity contains validated OIDC identity
	Identity services.OIDCIdentity `json:"identity"`
	// Web session will be generated by auth server if requested in OIDCAuthRequest
	Session *Session `json:"session,omitempty"`
	// Cert will be generated by certificate authority
	Cert []byte `json:"cert,omitempty"`
	// Req is original oidc auth request
	Req services.OIDCAuthRequest `json:"req"`
	// HostSigners is a list of signing host public keys
	// trusted by proxy, used in console login
	HostSigners []services.CertAuthority `json:"host_signers"`
}

// ValidateOIDCAuthCallback is called by the proxy to check OIDC query parameters
// returned by OIDC Provider, if everything checks out, auth server
// will respond with OIDCAuthResponse, otherwise it will return error
func (a *AuthServer) ValidateOIDCAuthCallback(q url.Values) (*OIDCAuthResponse, error) {
	if error := q.Get("error"); error != "" {
		return nil, trace.OAuth2(oauth2.ErrorInvalidRequest, error, q)
	}

	code := q.Get("code")
	if code == "" {
		return nil, trace.OAuth2(
			oauth2.ErrorInvalidRequest, "code query param must be set", q)
	}

	stateToken := q.Get("state")
	if stateToken == "" {
		return nil, trace.OAuth2(
			oauth2.ErrorInvalidRequest, "missing state query param", q)
	}

	req, err := a.Identity.GetOIDCAuthRequest(stateToken)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	connector, err := a.Identity.GetOIDCConnector(req.ConnectorID, true)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	oidcClient, err := a.getOIDCClient(connector)
	if err != nil {
		return nil, trace.Wrap(err)
	}

	tok, err := oidcClient.ExchangeAuthCode(code)
	if err != nil {
		return nil, trace.OAuth2(
			oauth2.ErrorUnsupportedResponseType,
			"unable to verify auth code with issuer", q)
	}

	claims, err := tok.Claims()
	if err != nil {
		return nil, trace.OAuth2(
			oauth2.ErrorUnsupportedResponseType, "unable to construct claims", q)
	}

	ident, err := oidc.IdentityFromClaims(claims)
	if err != nil {
		return nil, trace.OAuth2(
			oauth2.ErrorUnsupportedResponseType, "unable to convert claims to identity", q)
	}

	log.Infof("[IDENTITY] expires at: %v", ident.ExpiresAt)

	response := &OIDCAuthResponse{
		Identity: services.OIDCIdentity{ConnectorID: connector.ID, Email: ident.Email},
		Req:      *req,
	}

	if !req.CheckUser {
		return response, nil
	}

	user, err := a.Identity.GetUserByOIDCIdentity(services.OIDCIdentity{
		ConnectorID: req.ConnectorID, Email: ident.Email})
	if err != nil {
		return nil, trace.Wrap(err)
	}
	response.Username = user.GetName()

	if req.CreateWebSession {
		sess, err := a.NewWebSession(user.GetName())
		if err != nil {
			return nil, trace.Wrap(err)
		}
		sess.ExpiresAt = ident.ExpiresAt.UTC()
		sessionTTL := minTTL(toTTL(a.clock, ident.ExpiresAt), WebSessionTTL)
		if err := a.UpsertWebSession(user.GetName(), sess, sessionTTL); err != nil {
			return nil, trace.Wrap(err)
		}
		response.Session = sess
	}

	if len(req.PublicKey) != 0 {
		certTTL := minTTL(toTTL(a.clock, ident.ExpiresAt), req.CertTTL)
		cert, err := a.GenerateUserCert(req.PublicKey, user.GetName(), certTTL)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		response.Cert = cert

		authorities, err := a.GetCertAuthorities(services.HostCA, false)
		if err != nil {
			return nil, trace.Wrap(err)
		}
		for _, authority := range authorities {
			response.HostSigners = append(response.HostSigners, *authority)
		}
	}

	return response, nil
}

const (
	// WebSessionTTL specifies standard web session time to live
	WebSessionTTL = 10 * time.Minute
	// TokenLenBytes is len in bytes of the invite token
	TokenLenBytes = 16
	// WebSessionTokenLenBytes specifies len in bytes of the
	// web session random token
	WebSessionTokenLenBytes = 32
)

// minTTL finds min non 0 TTL duration,
// if both durations are 0, fails
func minTTL(a, b time.Duration) time.Duration {
	if a == 0 {
		return b
	}
	if b == 0 {
		return a
	}
	if a < b {
		return a
	}
	return b
}

// toTTL converts expiration time to TTL duration
// relative to current time as provided by clock
func toTTL(c clockwork.Clock, tm time.Time) time.Duration {
	now := c.Now().UTC()
	if tm.IsZero() || tm.Before(now) {
		return 0
	}
	return tm.Sub(now)
}