feat: add ldap support (#232)

* feat: add ldap support

* feat: add insecure option for self-signed certificates

* fix: recognize ldap as a username provider

* test: fix tests

* feat: add configurable search filter

* fix: fix error message in ldap search result

* refactor: bot suggestions

internal/ldap/ldap.go

@@ -0,0 +1,77 @@
+package ldap
+
+import (
+	"crypto/tls"
+	"fmt"
+	"tinyauth/internal/types"
+
+	ldapgo "github.com/go-ldap/ldap/v3"
+)
+
+type LDAP struct {
+	Config types.LdapConfig
+	Conn   *ldapgo.Conn
+	BaseDN string
+}
+
+func NewLDAP(config types.LdapConfig) (*LDAP, error) {
+	// Connect to the LDAP server
+	conn, err := ldapgo.DialURL(config.Address, ldapgo.DialWithTLSConfig(&tls.Config{
+		InsecureSkipVerify: config.Insecure,
+		MinVersion:         tls.VersionTLS12,
+	}))
+	if err != nil {
+		return nil, err
+	}
+
+	// Bind to the LDAP server with the provided credentials
+	err = conn.Bind(config.BindDN, config.BindPassword)
+	if err != nil {
+		return nil, err
+	}
+
+	return &LDAP{
+		Config: config,
+		Conn:   conn,
+		BaseDN: config.BaseDN,
+	}, nil
+}
+
+func (l *LDAP) Search(username string) (string, error) {
+	// Escape the username to prevent LDAP injection
+	escapedUsername := ldapgo.EscapeFilter(username)
+	filter := fmt.Sprintf(l.Config.SearchFilter, escapedUsername)
+
+	// Create a search request to find the user by username
+	searchRequest := ldapgo.NewSearchRequest(
+		l.BaseDN,
+		ldapgo.ScopeWholeSubtree, ldapgo.NeverDerefAliases, 0, 0, false,
+		filter,
+		[]string{"dn"},
+		nil,
+	)
+
+	// Perform the search
+	searchResult, err := l.Conn.Search(searchRequest)
+	if err != nil {
+		return "", err
+	}
+
+	if len(searchResult.Entries) != 1 {
+		return "", fmt.Errorf("err multiple or no entries found for user %s", username)
+	}
+
+	// User found, return the distinguished name (DN)
+	userDN := searchResult.Entries[0].DN
+
+	return userDN, nil
+}
+
+func (l *LDAP) Bind(userDN string, password string) error {
+	// Bind to the LDAP server with the user's DN and password
+	err := l.Conn.Bind(userDN, password)
+	if err != nil {
+		return err
+	}
+	return nil
+}