mox/http/autoconf.go

package http

import (
	"encoding/xml"
	"fmt"
	"net/http"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"

	"github.com/mjl-/mox/config"
	"github.com/mjl-/mox/mlog"
	"github.com/mjl-/mox/mox-"
	"github.com/mjl-/mox/smtp"
)

var (
	metricAutoconf = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "mox_autoconf_request_total",
			Help: "Number of autoconf requests.",
		},
		[]string{"domain"},
	)
	metricAutodiscover = promauto.NewCounterVec(
		prometheus.CounterOpts{
			Name: "mox_autodiscover_request_total",
			Help: "Number of autodiscover requests.",
		},
		[]string{"domain"},
	)
)

// Autoconfiguration/Autodiscovery:
//
//   - Thunderbird will request an "autoconfig" xml file.
//   - Microsoft tools will request an "autodiscovery" xml file.
//   - In my tests on an internal domain, iOS mail only talks to Apple servers, then
//   does not attempt autoconfiguration. Possibly due to them being private DNS names.
//
// DNS records seem optional, but autoconfig.<domain> and autodiscover.<domain>
// (both CNAME or A) are useful, and so is SRV _autodiscovery._tcp.<domain> 0 0 443
// autodiscover.<domain> (or just <hostname> directly).
//
// Autoconf/discovery only works with valid TLS certificates, not with self-signed
// certs. So use it on public endpoints with certs signed by common CA's, or run
// your own (internal) CA and import the CA cert on your devices.
//
// Also see https://roll.urown.net/server/mail/autoconfig.html

// Autoconfiguration for Mozilla Thunderbird.
// User should create a DNS record: autoconfig.<domain> (CNAME or A).
// See https://wiki.mozilla.org/Thunderbird:Autoconfiguration:ConfigFileFormat
func autoconfHandle(l config.Listener) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		log := xlog.WithContext(r.Context())

		var addrDom string
		defer func() {
			metricAutoconf.WithLabelValues(addrDom).Inc()
		}()

		email := r.FormValue("emailaddress")
		log.Debug("autoconfig request", mlog.Field("email", email))
		addr, err := smtp.ParseAddress(email)
		if err != nil {
			http.Error(w, "400 - bad request - invalid parameter emailaddress", http.StatusBadRequest)
			return
		}

		if _, ok := mox.Conf.Domain(addr.Domain); !ok {
			http.Error(w, "400 - bad request - unknown domain", http.StatusBadRequest)
			return
		}
		addrDom = addr.Domain.Name()

		hostname := l.HostnameDomain
		if hostname.IsZero() {
			hostname = mox.Conf.Static.HostnameDomain
		}

		// Thunderbird doesn't seem to allow U-labels, always return ASCII names.
		var resp autoconfigResponse
		resp.Version = "1.1"
		resp.EmailProvider.ID = addr.Domain.ASCII
		resp.EmailProvider.Domain = addr.Domain.ASCII
		resp.EmailProvider.DisplayName = email
		resp.EmailProvider.DisplayShortName = addr.Domain.ASCII

		var imapPort int
		var imapSocket string
		if l.IMAPS.Enabled {
			imapPort = config.Port(l.IMAPS.Port, 993)
			imapSocket = "SSL"
		} else if l.IMAP.Enabled {
			imapPort = config.Port(l.IMAP.Port, 143)
			if l.TLS != nil {
				imapSocket = "STARTTLS"
			} else {
				imapSocket = "plain"
			}
		} else {
			log.Error("autoconfig: no imap configured?")
		}

		// todo: specify SCRAM-SHA256 once thunderbird and autoconfig supports it. we could implement CRAM-MD5 and use it.

		resp.EmailProvider.IncomingServer.Type = "imap"
		resp.EmailProvider.IncomingServer.Hostname = hostname.ASCII
		resp.EmailProvider.IncomingServer.Port = imapPort
		resp.EmailProvider.IncomingServer.SocketType = imapSocket
		resp.EmailProvider.IncomingServer.Username = email
		resp.EmailProvider.IncomingServer.Authentication = "password-cleartext"

		var smtpPort int
		var smtpSocket string
		if l.Submissions.Enabled {
			smtpPort = config.Port(l.Submissions.Port, 465)
			smtpSocket = "SSL"
		} else if l.Submission.Enabled {
			smtpPort = config.Port(l.Submission.Port, 587)
			if l.TLS != nil {
				smtpSocket = "STARTTLS"
			} else {
				smtpSocket = "plain"
			}
		} else {
			log.Error("autoconfig: no smtp submission configured?")
		}

		resp.EmailProvider.OutgoingServer.Type = "smtp"
		resp.EmailProvider.OutgoingServer.Hostname = hostname.ASCII
		resp.EmailProvider.OutgoingServer.Port = smtpPort
		resp.EmailProvider.OutgoingServer.SocketType = smtpSocket
		resp.EmailProvider.OutgoingServer.Username = email
		resp.EmailProvider.OutgoingServer.Authentication = "password-cleartext"

		// todo: should we put the email address in the URL?
		resp.ClientConfigUpdate.URL = fmt.Sprintf("https://%s/mail/config-v1.1.xml", hostname.ASCII)

		w.Header().Set("Content-Type", "application/xml; charset=utf-8")
		enc := xml.NewEncoder(w)
		enc.Indent("", "\t")
		fmt.Fprint(w, xml.Header)
		if err := enc.Encode(resp); err != nil {
			log.Errorx("marshal autoconfig response", err)
		}
	}
}

// Autodiscover from Microsoft, also used by Thunderbird.
// User should create a DNS record: _autodiscover._tcp.<domain> IN SRV 0 0 443 <hostname or autodiscover.<domain>>
// In practice, autodiscover does not seem to work (any more). A connectivity test
// tool for outlook is available on https://testconnectivity.microsoft.com/, it has
// an option to do "Autodiscover to detect server settings". Incoming TLS
// connections are all failing, with various errors.
func autodiscoverHandle(l config.Listener) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		log := xlog.WithContext(r.Context())

		var addrDom string
		defer func() {
			metricAutodiscover.WithLabelValues(addrDom).Inc()
		}()

		if r.Method != "POST" {
			http.Error(w, "405 - method not allowed - post required", http.StatusMethodNotAllowed)
			return
		}

		var req autodiscoverRequest
		if err := xml.NewDecoder(r.Body).Decode(&req); err != nil {
			http.Error(w, "400 - bad request - parsing autodiscover request: "+err.Error(), http.StatusMethodNotAllowed)
			return
		}

		log.Debug("autodiscover request", mlog.Field("email", req.Request.EmailAddress))

		addr, err := smtp.ParseAddress(req.Request.EmailAddress)
		if err != nil {
			http.Error(w, "400 - bad request - invalid parameter emailaddress", http.StatusBadRequest)
			return
		}

		if _, ok := mox.Conf.Domain(addr.Domain); !ok {
			http.Error(w, "400 - bad request - unknown domain", http.StatusBadRequest)
			return
		}
		addrDom = addr.Domain.Name()

		hostname := l.HostnameDomain
		if hostname.IsZero() {
			hostname = mox.Conf.Static.HostnameDomain
		}

		// The docs are generated and fragmented in many tiny pages, hard to follow.
		// High-level starting point, https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxdscli/78530279-d042-4eb0-a1f4-03b18143cd19
		// Request: https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxdscli/2096fab2-9c3c-40b9-b123-edf6e8d55a9b
		// Response, protocol: https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxdscli/f4238db6-a983-435c-807a-b4b4a624c65b
		// It appears autodiscover does not allow specifying SCRAM-SHA256 as authentication method. See https://learn.microsoft.com/en-us/openspecs/exchange_server_protocols/ms-oxdscli/21fd2dd5-c4ee-485b-94fb-e7db5da93726

		var imapPort int
		imapSSL := "off"
		var imapEncryption string
		if l.IMAPS.Enabled {
			imapPort = config.Port(l.IMAPS.Port, 993)
			imapSSL = "on"
			imapEncryption = "TLS" // Assuming this means direct TLS.
		} else if l.IMAP.Enabled {
			imapPort = config.Port(l.IMAP.Port, 143)
			if l.TLS != nil {
				imapSSL = "on"
			}
		} else {
			log.Error("autoconfig: no imap configured?")
		}

		var smtpPort int
		smtpSSL := "off"
		var smtpEncryption string
		if l.Submissions.Enabled {
			smtpPort = config.Port(l.Submissions.Port, 465)
			smtpSSL = "on"
			smtpEncryption = "TLS" // Assuming this means direct TLS.
		} else if l.Submission.Enabled {
			smtpPort = config.Port(l.Submission.Port, 587)
			if l.TLS != nil {
				smtpSSL = "on"
			}
		} else {
			log.Error("autoconfig: no smtp submission configured?")
		}

		w.Header().Set("Content-Type", "application/xml; charset=utf-8")

		resp := autodiscoverResponse{}
		resp.XMLName.Local = "Autodiscover"
		resp.XMLName.Space = "http://schemas.microsoft.com/exchange/autodiscover/responseschema/2006"
		resp.Response.XMLName.Local = "Response"
		resp.Response.XMLName.Space = "http://schemas.microsoft.com/exchange/autodiscover/outlook/responseschema/2006a"
		resp.Response.Account = autodiscoverAccount{
			AccountType: "email",
			Action:      "settings",
			Protocol: []autodiscoverProtocol{
				{
					Type:         "IMAP",
					Server:       hostname.ASCII,
					Port:         imapPort,
					LoginName:    req.Request.EmailAddress,
					SSL:          imapSSL,
					Encryption:   imapEncryption,
					SPA:          "off", // Override default "on", this is Microsofts proprietary authentication protocol.
					AuthRequired: "on",
				},
				{
					Type:         "SMTP",
					Server:       hostname.ASCII,
					Port:         smtpPort,
					LoginName:    req.Request.EmailAddress,
					SSL:          smtpSSL,
					Encryption:   smtpEncryption,
					SPA:          "off", // Override default "on", this is Microsofts proprietary authentication protocol.
					AuthRequired: "on",
				},
			},
		}
		enc := xml.NewEncoder(w)
		enc.Indent("", "\t")
		fmt.Fprint(w, xml.Header)
		if err := enc.Encode(resp); err != nil {
			log.Errorx("marshal autodiscover response", err)
		}
	}
}

// Thunderbird requests these URLs for autoconfig/autodiscover:
// https://autoconfig.example.org/mail/config-v1.1.xml?emailaddress=user%40example.org
// https://autodiscover.example.org/autodiscover/autodiscover.xml
// https://example.org/.well-known/autoconfig/mail/config-v1.1.xml?emailaddress=user%40example.org
// https://example.org/autodiscover/autodiscover.xml
type autoconfigResponse struct {
	XMLName xml.Name `xml:"clientConfig"`
	Version string   `xml:"version,attr"`

	EmailProvider struct {
		ID               string `xml:"id,attr"`
		Domain           string `xml:"domain"`
		DisplayName      string `xml:"displayName"`
		DisplayShortName string `xml:"displayShortName"`

		IncomingServer struct {
			Type           string `xml:"type,attr"`
			Hostname       string `xml:"hostname"`
			Port           int    `xml:"port"`
			SocketType     string `xml:"socketType"`
			Username       string `xml:"username"`
			Authentication string `xml:"authentication"`
		} `xml:"incomingServer"`

		OutgoingServer struct {
			Type           string `xml:"type,attr"`
			Hostname       string `xml:"hostname"`
			Port           int    `xml:"port"`
			SocketType     string `xml:"socketType"`
			Username       string `xml:"username"`
			Authentication string `xml:"authentication"`
		} `xml:"outgoingServer"`
	} `xml:"emailProvider"`

	ClientConfigUpdate struct {
		URL string `xml:"url,attr"`
	} `xml:"clientConfigUpdate"`
}

type autodiscoverRequest struct {
	XMLName xml.Name `xml:"Autodiscover"`
	Request struct {
		EmailAddress             string `xml:"EMailAddress"`
		AcceptableResponseSchema string `xml:"AcceptableResponseSchema"`
	}
}

type autodiscoverResponse struct {
	XMLName  xml.Name
	Response struct {
		XMLName xml.Name
		Account autodiscoverAccount
	}
}

type autodiscoverAccount struct {
	AccountType string
	Action      string
	Protocol    []autodiscoverProtocol
}

type autodiscoverProtocol struct {
	Type          string
	Server        string
	Port          int
	DirectoryPort int
	ReferralPort  int
	LoginName     string
	SSL           string
	Encryption    string `xml:",omitempty"`
	SPA           string
	AuthRequired  string
}