bagage/auth_ldap.go

package main

import (
	"errors"
	"fmt"
	"net/http"

	"github.com/go-ldap/ldap/v3"
)

/* Check credentials against LDAP */
type LdapPreAuth struct {
	WithConfig      *Config
	OnWrongPassword ErrorHandler
	OnFailure       ErrorHandler
	OnCreds         CredsHandler
}

func (l LdapPreAuth) WithCreds(username, password string) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		var e *LdapWrongPasswordError

		access_key, secret_key, err := LdapGetS3(l.WithConfig, username, password)
		
		if err == nil {
			l.OnCreds.WithCreds(access_key, secret_key).ServeHTTP(w, r)
		} else if errors.As(err, &e) {
			l.OnWrongPassword.WithError(err).ServeHTTP(w, r)
		} else {
			l.OnFailure.WithError(e).ServeHTTP(w, r)
		}
	})
}

/**
 * Private logic
 */

type ldapConnector struct {
	conn   *ldap.Conn
	config *Config
	userDn string
}

type LdapError struct {
	Username string
	Err error
}
func (e *LdapError) Error() string { return "ldap error for "+e.Username+": "+e.Err.Error() }
type LdapWrongPasswordError struct { LdapError }

func LdapGetS3(c *Config, username, password string) (access_key, secret_key string, werr error) {
	// 1. Connect to the server
	conn, err := ldapConnect(c)
	if err != nil {
		werr = &LdapError { username, err }
		return
	}
	defer conn.Close()

	// 2. Authenticate with provided credentials
	// @FIXME we should better check the error, it could also be due to an LDAP error
	err = conn.auth(username, password)
	if err != nil {
		werr = &LdapWrongPasswordError { LdapError { username, err } }
		return
	}

	// 3. Fetch user's profile
	profile, err := conn.profile()
	if err != nil {
		werr = &LdapError { username, err }
		return
	}

	// 4. Basic checks upon users' attributes
	access_key = profile.GetAttributeValue("garage_s3_access_key")
	secret_key = profile.GetAttributeValue("garage_s3_secret_key")
	if access_key == "" || secret_key == "" {
		err = errors.New(fmt.Sprintf("Either access key or secret key is missing in LDAP for %s", conn.userDn))
		werr = &LdapError { username, err }
		return
	}

	// 5. Send fetched credentials to the next middleware
	return
}

func ldapConnect(c *Config) (ldapConnector, error) {
	ldapSock, err := ldap.Dial("tcp", c.LdapServer)
	if err != nil {
		return ldapConnector{}, err
	}

	return ldapConnector{
		conn:   ldapSock,
		config: c,
	}, nil
}

func (l *ldapConnector) auth(username, password string) error {
	l.userDn = fmt.Sprintf("%s=%s,%s", l.config.UserNameAttr, username, l.config.UserBaseDN)
	return l.conn.Bind(l.userDn, password)
}

func (l *ldapConnector) profile() (*ldap.Entry, error) {
	searchRequest := ldap.NewSearchRequest(
		l.userDn,
		ldap.ScopeBaseObject,
		ldap.NeverDerefAliases,
		0,
		0,
		false,
		"(objectClass=*)",
		[]string{"garage_s3_access_key", "garage_s3_secret_key"},
		nil)

	sr, err := l.conn.Search(searchRequest)
	if err != nil {
		return nil, err
	}

	if len(sr.Entries) != 1 {
		return nil, errors.New(fmt.Sprintf("Wrong number of LDAP entries, expected 1, got %d", len(sr.Entries)))
	}

	return sr.Entries[0], nil
}

func (l *ldapConnector) Close() {
	if l.conn != nil {
		l.conn.Close()
		l.conn = nil
	}
}