constants.go

/*
Copyright 2018-2019 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 teleport

import (
	"fmt"
	"strings"
	"time"

	"github.com/coreos/go-semver/semver"
)

// WebAPIVersion is a current webapi version
const WebAPIVersion = "v1"

const (
	// SSHAuthSock is the environment variable pointing to the
	// Unix socket the SSH agent is running on.
	SSHAuthSock = "SSH_AUTH_SOCK"
	// SSHAgentPID is the environment variable pointing to the agent
	// process ID
	SSHAgentPID = "SSH_AGENT_PID"

	// SSHTeleportUser is the current Teleport user that is logged in.
	SSHTeleportUser = "SSH_TELEPORT_USER"

	// SSHSessionWebproxyAddr is the address the web proxy.
	SSHSessionWebproxyAddr = "SSH_SESSION_WEBPROXY_ADDR"

	// SSHTeleportClusterName is the name of the cluster this node belongs to.
	SSHTeleportClusterName = "SSH_TELEPORT_CLUSTER_NAME"

	// SSHTeleportHostUUID is the UUID of the host.
	SSHTeleportHostUUID = "SSH_TELEPORT_HOST_UUID"

	// SSHSessionID is the UUID of the current session.
	SSHSessionID = "SSH_SESSION_ID"
)

const (
	// HTTPNextProtoTLS is the NPN/ALPN protocol negotiated during
	// HTTP/1.1.'s TLS setup.
	// https://www.iana.org/assignments/tls-extensiontype-values/tls-extensiontype-values.xhtml#alpn-protocol-ids
	HTTPNextProtoTLS = "http/1.1"
)

const (
	// TOTPValidityPeriod is the number of seconds a TOTP token is valid.
	TOTPValidityPeriod uint = 30

	// TOTPSkew adds that many periods before and after to the validity window.
	TOTPSkew uint = 1
)

const (
	// ComponentMemory is a memory backend
	ComponentMemory = "memory"

	// ComponentAuthority is a TLS and an SSH certificate authority
	ComponentAuthority = "ca"

	// ComponentProcess is a main control process
	ComponentProcess = "proc"

	// ComponentServer is a server subcomponent of some services
	ComponentServer = "server"

	// ComponentACME is ACME protocol controller
	ComponentACME = "acme"

	// ComponentReverseTunnelServer is reverse tunnel server
	// that together with agent establish a bi-directional SSH revers tunnel
	// to bypass firewall restrictions
	ComponentReverseTunnelServer = "proxy:server"

	// ComponentReverseTunnelAgent is reverse tunnel agent
	// that together with server establish a bi-directional SSH revers tunnel
	// to bypass firewall restrictions
	ComponentReverseTunnelAgent = "proxy:agent"

	// ComponentLabel is a component label name used in reporting
	ComponentLabel = "component"

	// ComponentProxyKube is a kubernetes proxy
	ComponentProxyKube = "proxy:kube"

	// ComponentAuth is the cluster CA node (auth server API)
	ComponentAuth = "auth"

	// ComponentGRPC is grpc server
	ComponentGRPC = "grpc"

	// ComponentMigrate is responsible for data migrations
	ComponentMigrate = "migrate"

	// ComponentNode is SSH node (SSH server serving requests)
	ComponentNode = "node"

	// ComponentForwardingNode is SSH node (SSH server serving requests)
	ComponentForwardingNode = "node:forward"

	// ComponentProxy is SSH proxy (SSH server forwarding connections)
	ComponentProxy = "proxy"

	// ComponentProxyPeer is the proxy peering component of the proxy service
	ComponentProxyPeer = "proxy:peer"

	// ComponentApp is the application proxy service.
	ComponentApp = "app:service"

	// ComponentDatabase is the database proxy service.
	ComponentDatabase = "db:service"

	// ComponentDiscovery is the Discovery service.
	ComponentDiscovery = "discovery:service"

	// ComponentAppProxy is the application handler within the web proxy service.
	ComponentAppProxy = "app:web"

	// ComponentWebProxy is the web handler within the web proxy service.
	ComponentWebProxy = "web"

	// ComponentDiagnostic is a diagnostic service
	ComponentDiagnostic = "diag"

	// ComponentClient is a client
	ComponentClient = "client"

	// ComponentTunClient is a tunnel client
	ComponentTunClient = "client:tunnel"

	// ComponentCache is a cache component
	ComponentCache = "cache"

	// ComponentBackend is a backend component
	ComponentBackend = "backend"

	// ComponentSubsystemProxy is the proxy subsystem.
	ComponentSubsystemProxy = "subsystem:proxy"

	// ComponentSubsystemSFTP is the SFTP subsystem.
	ComponentSubsystemSFTP = "subsystem:sftp"

	// ComponentLocalTerm is a terminal on a regular SSH node.
	ComponentLocalTerm = "term:local"

	// ComponentRemoteTerm is a terminal on a forwarding SSH node.
	ComponentRemoteTerm = "term:remote"

	// ComponentRemoteSubsystem is subsystem on a forwarding SSH node.
	ComponentRemoteSubsystem = "subsystem:remote"

	// ComponentAuditLog is audit log component
	ComponentAuditLog = "audit"

	// ComponentKeyAgent is an agent that has loaded the sessions keys and
	// certificates for a user connected to a proxy.
	ComponentKeyAgent = "keyagent"

	// ComponentKeyStore is all sessions keys and certificates a user has on disk
	// for all proxies.
	ComponentKeyStore = "keystore"

	// ComponentConnectProxy is the HTTP CONNECT proxy used to tunnel connection.
	ComponentConnectProxy = "http:proxy"

	// ComponentSOCKS is a SOCKS5 proxy.
	ComponentSOCKS = "socks"

	// ComponentKeyGen is the public/private keypair generator.
	ComponentKeyGen = "keygen"

	// ComponentFirestore represents firestore clients
	ComponentFirestore = "firestore"

	// ComponentSession is an active session.
	ComponentSession = "session"

	// ComponentDynamoDB represents dynamodb clients
	ComponentDynamoDB = "dynamodb"

	// Component pluggable authentication module (PAM)
	ComponentPAM = "pam"

	// ComponentUpload is a session recording upload server
	ComponentUpload = "upload"

	// ComponentWeb is a web server
	ComponentWeb = "web"

	// ComponentWebsocket is websocket server that the web client connects to.
	ComponentWebsocket = "websocket"

	// ComponentRBAC is role-based access control.
	ComponentRBAC = "rbac"

	// ComponentKeepAlive is keep-alive messages sent from clients to servers
	// and vice versa.
	ComponentKeepAlive = "keepalive"

	// ComponentTeleport is the "teleport" binary.
	ComponentTeleport = "teleport"

	// ComponentTSH is the "tsh" binary.
	ComponentTSH = "tsh"

	// ComponentTBot is the "tbot" binary
	ComponentTBot = "tbot"

	// ComponentKubeClient is the Kubernetes client.
	ComponentKubeClient = "client:kube"

	// ComponentBuffer is in-memory event circular buffer
	// used to broadcast events to subscribers.
	ComponentBuffer = "buffer"

	// ComponentBPF is the eBPF packagae.
	ComponentBPF = "bpf"

	// ComponentRestrictedSession is restriction of user access to kernel objects
	ComponentRestrictedSession = "restrictedsess"

	// ComponentCgroup is the cgroup package.
	ComponentCgroup = "cgroups"

	// ComponentKube is an Kubernetes API gateway.
	ComponentKube = "kubernetes"

	// ComponentSAML is a SAML service provider.
	ComponentSAML = "saml"

	// ComponentMetrics is a metrics server
	ComponentMetrics = "metrics"

	// ComponentWindowsDesktop is a Windows desktop access server.
	ComponentWindowsDesktop = "windows_desktop"

	// ComponentTracing is a tracing exporter
	ComponentTracing = "tracing"

	// ComponentInstance is an abstract component common to all services.
	ComponentInstance = "instance"

	// ComponentVersionControl is the component common to all version control operations.
	ComponentVersionControl = "version-control"

	// ComponentUsageReporting is the component responsible for reporting usage metrics.
	ComponentUsageReporting = "usage-reporting"

	// ComponentAthena represents athena clients.
	ComponentAthena = "athena"

	// VerboseLogEnvVar forces all logs to be verbose (down to DEBUG level)
	VerboseLogsEnvVar = "TELEPORT_DEBUG"

	// IterationsEnvVar sets tests iterations to run
	IterationsEnvVar = "ITERATIONS"

	// DefaultTerminalWidth defines the default width of a server-side allocated
	// pseudo TTY
	DefaultTerminalWidth = 80

	// DefaultTerminalHeight defines the default height of a server-side allocated
	// pseudo TTY
	DefaultTerminalHeight = 25

	// SafeTerminalType is the fall-back TTY type to fall back to (when $TERM
	// is not defined)
	SafeTerminalType = "xterm"

	// DataDirParameterName is the name of the data dir configuration parameter passed
	// to all backends during initialization
	DataDirParameterName = "data_dir"

	// KeepAliveReqType is a SSH request type to keep the connection alive. A client and
	// a server keep pining each other with it.
	KeepAliveReqType = "keepalive@openssh.com"

	// ClusterDetailsReqType is the name of a global request which returns cluster details like
	// if the proxy is recording sessions or not and if FIPS is enabled.
	ClusterDetailsReqType = "cluster-details@goteleport.com"

	// JSON means JSON serialization format
	JSON = "json"

	// YAML means YAML serialization format
	YAML = "yaml"

	// Text means text serialization format
	Text = "text"

	// PTY is a raw PTY session capture format
	PTY = "pty"

	// Names is for formatting node names in plain text
	Names = "names"

	// LinuxAdminGID is the ID of the standard adm group on linux
	LinuxAdminGID = 4

	// DirMaskSharedGroup is the mask for a directory accessible
	// by the owner and group
	DirMaskSharedGroup = 0o770

	// FileMaskOwnerOnly is the file mask that allows read write access
	// to owers only
	FileMaskOwnerOnly = 0o600

	// On means mode is on
	On = "on"

	// Off means mode is off
	Off = "off"

	// GCSTestURI turns on GCS tests
	GCSTestURI = "TEST_GCS_URI"

	// AWSRunTests turns on tests executed against AWS directly
	AWSRunTests = "TEST_AWS"

	// Region is AWS region parameter
	Region = "region"

	// Endpoint is an optional Host for non-AWS S3
	Endpoint = "endpoint"

	// Insecure is an optional switch to use HTTP instead of HTTPS
	Insecure = "insecure"

	// DisableServerSideEncryption is an optional switch to opt out of SSE in case the provider does not support it
	DisableServerSideEncryption = "disablesse"

	// ACL is the canned ACL to send to S3
	ACL = "acl"

	// SSEKMSKey is an optional switch to use an KMS CMK key for S3 SSE.
	SSEKMSKey = "sse_kms_key"

	// SchemeFile configures local disk-based file storage for audit events
	SchemeFile = "file"

	// SchemeStdout outputs audit log entries to stdout
	SchemeStdout = "stdout"

	// SchemeS3 is used for S3-like object storage
	SchemeS3 = "s3"

	// SchemeGCS is used for Google Cloud Storage
	SchemeGCS = "gs"

	// LogsDir is a log subdirectory for events and logs
	LogsDir = "log"

	// Syslog is a mode for syslog logging
	Syslog = "syslog"

	// HumanDateFormat is a human readable date formatting
	HumanDateFormat = "Jan _2 15:04 UTC"

	// HumanDateFormatMilli is a human readable date formatting with milliseconds
	HumanDateFormatMilli = "Jan _2 15:04:05.000 UTC"

	// DebugLevel is a debug logging level name
	DebugLevel = "debug"

	// MinimumEtcdVersion is the minimum version of etcd supported by Teleport
	MinimumEtcdVersion = "3.3.0"
)

const (
	// These values are from https://openid.net/specs/openid-connect-core-1_0.html#AuthRequest

	// OIDCPromptSelectAccount instructs the Authorization Server to
	// prompt the End-User to select a user account.
	OIDCPromptSelectAccount = "select_account"

	// OIDCAccessTypeOnline indicates that OIDC flow should be performed
	// with Authorization server and user connected online
	OIDCAccessTypeOnline = "online"
)

// Component generates "component:subcomponent1:subcomponent2" strings used
// in debugging
func Component(components ...string) string {
	return strings.Join(components, ":")
}

const (
	// AuthorizedKeys are public keys that check against User CAs.
	AuthorizedKeys = "authorized_keys"
	// KnownHosts are public keys that check against Host CAs.
	KnownHosts = "known_hosts"
)

const (
	// CertExtensionPermitX11Forwarding allows X11 forwarding for certificate
	CertExtensionPermitX11Forwarding = "permit-X11-forwarding"
	// CertExtensionPermitAgentForwarding allows agent forwarding for certificate
	CertExtensionPermitAgentForwarding = "permit-agent-forwarding"
	// CertExtensionPermitPTY allows user to request PTY
	CertExtensionPermitPTY = "permit-pty"
	// CertExtensionPermitPortForwarding allows user to request port forwarding
	CertExtensionPermitPortForwarding = "permit-port-forwarding"
	// CertExtensionTeleportRoles is used to propagate teleport roles
	CertExtensionTeleportRoles = "teleport-roles"
	// CertExtensionTeleportRouteToCluster is used to encode
	// the target cluster to route to in the certificate
	CertExtensionTeleportRouteToCluster = "teleport-route-to-cluster"
	// CertExtensionTeleportTraits is used to propagate traits about the user.
	CertExtensionTeleportTraits = "teleport-traits"
	// CertExtensionTeleportActiveRequests is used to track which privilege
	// escalation requests were used to construct the certificate.
	CertExtensionTeleportActiveRequests = "teleport-active-requests"
	// CertExtensionMFAVerified is used to mark certificates issued after an MFA
	// check.
	CertExtensionMFAVerified = "mfa-verified"
	// CertExtensionPreviousIdentityExpires is the extension that stores an RFC3339
	// timestamp representing the expiry time of the identity/cert that this
	// identity/cert was derived from. It is used to determine a session's hard
	// deadline in cases where both require_session_mfa and disconnect_expired_cert
	// are enabled. See https://github.com/gravitational/teleport/issues/18544.
	CertExtensionPreviousIdentityExpires = "prev-identity-expires"
	// CertExtensionLoginIP is used to embed the IP of the client that created
	// the certificate.
	CertExtensionLoginIP = "login-ip"
	// CertExtensionImpersonator is set when one user has requested certificates
	// for another user
	CertExtensionImpersonator = "impersonator"
	// CertExtensionDisallowReissue is set when a certificate should not be allowed
	// to request future certificates.
	CertExtensionDisallowReissue = "disallow-reissue"
	// CertExtensionRenewable is a flag to indicate the certificate may be
	// renewed.
	CertExtensionRenewable = "renewable"
	// CertExtensionGeneration counts the number of times a certificate has
	// been renewed.
	CertExtensionGeneration = "generation"
	// CertExtensionAllowedResources lists the resources which this certificate
	// should be allowed to access
	CertExtensionAllowedResources = "teleport-allowed-resources"
	// CertExtensionConnectionDiagnosticID contains the ID of the ConnectionDiagnostic.
	// The Node/Agent will append connection traces to this diagnostic instance.
	CertExtensionConnectionDiagnosticID = "teleport-connection-diagnostic-id"
	// CertExtensionPrivateKeyPolicy is used to mark certificates with their supported
	// private key policy.
	CertExtensionPrivateKeyPolicy = "private-key-policy"
	// CertExtensionDeviceID is the trusted device identifier.
	CertExtensionDeviceID = "teleport-device-id"
	// CertExtensionDeviceAssetTag is the device inventory identifier.
	CertExtensionDeviceAssetTag = "teleport-device-asset-tag"
	// CertExtensionDeviceCredentialID is the identifier for the credential used
	// by the device to authenticate itself.
	CertExtensionDeviceCredentialID = "teleport-device-credential-id"
)

// Note: when adding new providers to this list, consider updating the help message for --provider flag
// for `tctl sso configure oidc` and `tctl sso configure saml` commands
// as well as docs at https://goteleport.com/docs/enterprise/sso/#provider-specific-workarounds
const (
	// NetIQ is an identity provider.
	NetIQ = "netiq"
	// ADFS is Microsoft Active Directory Federation Services
	ADFS = "adfs"
	// Ping is the common backend for all Ping Identity-branded identity
	// providers (including PingOne, PingFederate, etc).
	Ping = "ping"
	// Okta should be used for Okta OIDC providers.
	Okta = "okta"
	// JumpCloud is an identity provider.
	JumpCloud = "jumpcloud"
)

const (
	// RemoteCommandSuccess is returned when a command has successfully executed.
	RemoteCommandSuccess = 0
	// RemoteCommandFailure is returned when a command has failed to execute and
	// we don't have another status code for it.
	RemoteCommandFailure = 255
	// HomeDirNotFound is returned when a the "teleport checkhomedir" command cannot
	// find the user's home directory.
	HomeDirNotFound = 254
)

// MaxEnvironmentFileLines is the maximum number of lines in a environment file.
const MaxEnvironmentFileLines = 1000

// MaxResourceSize is the maximum size (in bytes) of a serialized resource.  This limit is
// typically only enforced against resources that are likely to arbitrarily grow (e.g. PluginData).
const MaxResourceSize = 1000000

// MaxHTTPRequestSize is the maximum accepted size (in bytes) of the body of
// a received HTTP request.  This limit is meant to be used with utils.ReadAtMost
// to prevent resource exhaustion attacks.
const MaxHTTPRequestSize = 10 * 1024 * 1024

// MaxHTTPResponseSize is the maximum accepted size (in bytes) of the body of
// a received HTTP response.  This limit is meant to be used with utils.ReadAtMost
// to prevent resource exhaustion attacks.
const MaxHTTPResponseSize = 10 * 1024 * 1024

const (
	// CertificateFormatOldSSH is used to make Teleport interoperate with older
	// versions of OpenSSH.
	CertificateFormatOldSSH = "oldssh"

	// CertificateFormatUnspecified is used to check if the format was specified
	// or not.
	CertificateFormatUnspecified = ""
)

const (
	// TraitInternalPrefix is the role variable prefix that indicates it's for
	// local accounts.
	TraitInternalPrefix = "internal"

	// TraitExternalPrefix is the role variable prefix that indicates the data comes from an external identity provider.
	TraitExternalPrefix = "external"

	// TraitTeams is the name of the role variable use to store team
	// membership information
	TraitTeams = "github_teams"

	// TraitJWT is the name of the trait containing JWT header for app access.
	TraitJWT = "jwt"

	// TraitInternalLoginsVariable is the variable used to store allowed
	// logins for local accounts.
	TraitInternalLoginsVariable = "{{internal.logins}}"

	// TraitInternalWindowsLoginsVariable is the variable used to store
	// allowed Windows Desktop logins for local accounts.
	TraitInternalWindowsLoginsVariable = "{{internal.windows_logins}}"

	// TraitInternalKubeGroupsVariable is the variable used to store allowed
	// kubernetes groups for local accounts.
	TraitInternalKubeGroupsVariable = "{{internal.kubernetes_groups}}"

	// TraitInternalKubeUsersVariable is the variable used to store allowed
	// kubernetes users for local accounts.
	TraitInternalKubeUsersVariable = "{{internal.kubernetes_users}}"

	// TraitInternalDBNamesVariable is the variable used to store allowed
	// database names for local accounts.
	TraitInternalDBNamesVariable = "{{internal.db_names}}"

	// TraitInternalDBUsersVariable is the variable used to store allowed
	// database users for local accounts.
	TraitInternalDBUsersVariable = "{{internal.db_users}}"

	// TraitInternalAWSRoleARNs is the variable used to store allowed AWS
	// role ARNs for local accounts.
	TraitInternalAWSRoleARNs = "{{internal.aws_role_arns}}"

	// TraitInternalAzureIdentities is the variable used to store allowed
	// Azure identities for local accounts.
	TraitInternalAzureIdentities = "{{internal.azure_identities}}"

	// TraitInternalGCPServiceAccounts is the variable used to store allowed
	// GCP service accounts for local accounts.
	TraitInternalGCPServiceAccounts = "{{internal.gcp_service_accounts}}"

	// TraitInternalJWTVariable is the variable used to store JWT token for
	// app sessions.
	TraitInternalJWTVariable = "{{internal.jwt}}"
)

// SCP is Secure Copy.
const SCP = "scp"

// AdminRoleName is the name of the default admin role for all local users if
// another role is not explicitly assigned
const AdminRoleName = "admin"

const (
	// PresetEditorRoleName is a name of a preset role that allows
	// editing cluster configuration.
	PresetEditorRoleName = "editor"

	// PresetAccessRoleName is a name of a preset role that allows
	// accessing cluster resources.
	PresetAccessRoleName = "access"

	// PresetAuditorRoleName is a name of a preset role that allows
	// reading cluster events and playing back session records.
	PresetAuditorRoleName = "auditor"
)

var PresetRoles = []string{PresetEditorRoleName, PresetAccessRoleName, PresetAuditorRoleName}

// MinClientVersion is the minimum client version required by the server.
var MinClientVersion string

func init() {
	// Per https://github.com/gravitational/teleport/blob/master/rfd/0012-teleport-versioning.md,
	// only one major version backwards is supported for clients.
	ver := semver.New(Version)
	MinClientVersion = fmt.Sprintf("%d.0.0", ver.Major-1)
}

const (
	// RemoteClusterStatusOffline indicates that cluster is considered as
	// offline, since it has missed a series of heartbeats
	RemoteClusterStatusOffline = "offline"
	// RemoteClusterStatusOnline indicates that cluster is sending heartbeats
	// at expected interval
	RemoteClusterStatusOnline = "online"
)

const (
	// SharedDirMode is a mode for a directory shared with group
	SharedDirMode = 0o750

	// PrivateDirMode is a mode for private directories
	PrivateDirMode = 0o700
)

const (
	// SessionEvent is sent by servers to clients when an audit event occurs on
	// the session.
	SessionEvent = "x-teleport-event"

	// VersionRequest is sent by clients to server requesting the Teleport
	// version they are running.
	VersionRequest = "x-teleport-version"

	// ForceTerminateRequest is an SSH request to forcefully terminate a session.
	ForceTerminateRequest = "x-teleport-force-terminate"

	// TerminalSizeRequest is a request for the terminal size of the session.
	TerminalSizeRequest = "x-teleport-terminal-size"

	// MFAPresenceRequest is an SSH request to notify clients that MFA presence is required for a session.
	MFAPresenceRequest = "x-teleport-mfa-presence"

	// EnvSSHJoinMode is the SSH environment variable that contains the requested participant mode.
	EnvSSHJoinMode = "TELEPORT_SSH_JOIN_MODE"

	// EnvSSHSessionReason is a reason attached to started sessions meant to describe their intent.
	EnvSSHSessionReason = "TELEPORT_SESSION_REASON"

	// EnvSSHSessionInvited is an environment variable listning people invited to a session.
	EnvSSHSessionInvited = "TELEPORT_SESSION_JOIN_MODE"

	// EnvSSHSessionDisplayParticipantRequirements is set to true or false to indicate if participant
	// requirement information should be printed.
	EnvSSHSessionDisplayParticipantRequirements = "TELEPORT_SESSION_PARTICIPANT_REQUIREMENTS"

	// SSHSessionJoinPrincipal is the SSH principal used when joining sessions.
	// This starts with a hyphen so it isn't a valid unix login.
	SSHSessionJoinPrincipal = "-teleport-internal-join"
)

const (
	// EnvKubeConfig is environment variable for kubeconfig
	EnvKubeConfig = "KUBECONFIG"

	// KubeConfigDir is a default directory where k8s stores its user local config
	KubeConfigDir = ".kube"

	// KubeConfigFile is a default filename where k8s stores its user local config
	KubeConfigFile = "config"

	// KubeRunTests turns on kubernetes tests
	KubeRunTests = "TEST_KUBE"

	// KubeSystemAuthenticated is a builtin group that allows
	// any user to access common API methods, e.g. discovery methods
	// required for initial client usage
	KubeSystemAuthenticated = "system:authenticated"

	// UsageKubeOnly specifies certificate usage metadata
	// that limits certificate to be only used for kubernetes proxying
	UsageKubeOnly = "usage:kube"

	// UsageAppOnly specifies a certificate metadata that only allows it to be
	// used for proxying applications.
	UsageAppsOnly = "usage:apps"

	// UsageDatabaseOnly specifies certificate usage metadata that only allows
	// it to be used for proxying database connections.
	UsageDatabaseOnly = "usage:db"

	// UsageWindowsDesktopOnly specifies certificate usage metadata that limits
	// certificate to be only used for Windows desktop access
	UsageWindowsDesktopOnly = "usage:windows_desktop"
)

const (
	// NodeIsAmbiguous serves as an identifying error string indicating that
	// the proxy subsystem found multiple nodes matching the specified hostname.
	NodeIsAmbiguous = "err-node-is-ambiguous"

	// MaxLeases serves as an identifying error string indicating that the
	// semaphore system is rejecting an acquisition attempt due to max
	// leases having already been reached.
	MaxLeases = "err-max-leases"
)

const (
	// OpenBrowserLinux is the command used to open a web browser on Linux.
	OpenBrowserLinux = "xdg-open"

	// OpenBrowserDarwin is the command used to open a web browser on macOS/Darwin.
	OpenBrowserDarwin = "open"

	// OpenBrowserWindows is the command used to open a web browser on Windows.
	OpenBrowserWindows = "rundll32.exe"

	// BrowserNone is the string used to suppress the opening of a browser in
	// response to 'tsh login' commands.
	BrowserNone = "none"
)

const (
	// ExecSubCommand is the sub-command Teleport uses to re-exec itself for
	// command execution (exec and shells).
	ExecSubCommand = "exec"

	// ForwardSubCommand is the sub-command Teleport uses to re-exec itself
	// for port forwarding.
	ForwardSubCommand = "forward"

	// CheckHomeDirSubCommand is the sub-command Teleport uses to re-exec itself
	// to check if the user's home directory exists.
	CheckHomeDirSubCommand = "checkhomedir"

	// ParkSubCommand is the sub-command Teleport uses to re-exec itself as a
	// specific UID to prevent the matching user from being deleted before
	// spawning the intended child process.
	ParkSubCommand = "park"

	// SFTPSubCommand is the sub-command Teleport uses to re-exec itself to
	// handle SFTP connections.
	SFTPSubCommand = "sftp"

	// WaitSubCommand is the sub-command Teleport uses to wait
	// until a domain name stops resolving. Its main use is to ensure no
	// auth instances are still running the previous major version.
	WaitSubCommand = "wait"
)

const (
	// ChanDirectTCPIP is a SSH channel of type "direct-tcpip".
	ChanDirectTCPIP = "direct-tcpip"

	// ChanSession is a SSH channel of type "session".
	ChanSession = "session"
)

const (
	// GetHomeDirSubsystem is an SSH subsystem request that Teleport
	// uses to get the home directory of a remote user.
	GetHomeDirSubsystem = "gethomedir"
)

// A principal name for use in SSH certificates.
type Principal string

const (
	// The localhost domain, for talking to a proxy or node on the same
	// machine.
	PrincipalLocalhost Principal = "localhost"
	// The IPv4 loopback address, for talking to a proxy or node on the same
	// machine.
	PrincipalLoopbackV4 Principal = "127.0.0.1"
	// The IPv6 loopback address, for talking to a proxy or node on the same
	// machine.
	PrincipalLoopbackV6 Principal = "::1"
)

// UserSystem defines a user as system.
const UserSystem = "system"

const (
	// internal application being proxied.
	AppJWTHeader = "teleport-jwt-assertion"

	// AppCFHeader is a compatibility header.
	AppCFHeader = "cf-access-token"

	// HostHeader is the name of the Host header.
	HostHeader = "Host"
)

// UserSingleUseCertTTL is a TTL for per-connection user certificates.
const UserSingleUseCertTTL = time.Minute

// StandardHTTPSPort is the default port used for the https URI scheme,
// cf. RFC 7230 § 2.7.2.
const StandardHTTPSPort = 443

const (
	// KubeSessionDisplayParticipantRequirementsQueryParam is the query parameter used to
	// indicate that the client wants to display the participant requirements
	// for the given session.
	KubeSessionDisplayParticipantRequirementsQueryParam = "displayParticipantRequirements"
	// KubeSessionReasonQueryParam is the query parameter used to indicate the reason
	// for the session request.
	KubeSessionReasonQueryParam = "reason"
	// KubeSessionInvitedQueryParam is the query parameter used to indicate the users
	// to invite to the session.
	KubeSessionInvitedQueryParam = "invite"
)