Best Practices and Approaches while implementing pure functional Scala code which is dependent on impure code/libraries

I am currently Implementing business logic code which is dependent on the custom scala library which has a lot of impure functions and we have a lot of code with is dependent on this library and cannot refactor as it will affect others. So I am trying to write my scala code as pure as possible and need suggestions for few use cases.

I have an LDAP utility library that does the following Authenticate based on username and password and returns Boolean, However, if there is a Connection exception or user not found it directly throws an exception. Reading and updating data based on UUID and parameters like first name and last name does pretty much the same thing My approach for the authentication use case is below

  def authenticateToUpdate(userName:String,password:String):Option[Boolean] =
    Some(ldapService.authenticate(username,password))

// or using either type to get the message as well
  def authenticateToUpdate(userName:String,password:String):Either[String,Boolean]=
    (ldapService.authenticate(username,password)) match {
      case true => Right(true)
      case false => Left("Validation failed, Invalid Password")
      case exception: Exception => Left(exception.toString)
    }

//##for Some type
  authenticateToUpdate(userName,password).fold(InvalidPassword)(updateOrder(orderId,userName))

//##for Either type
// Looking into how to implement

So I want to write my code as functional and close to pure function as possible need help and suggestions on how can I approach such scenario to write functional scala code.

As Tim says, when handling errors in Scala the easiest thing to do is to wrap the exception-throwing code in a Try block. For example:

import scala.util.{Try, Success, Failure}

Try {
  connector.makeCall()
} match {
  case Success(value) if value => Right("yay")
  case Success(value)          => Left("☹️")
  case Failure(ex)             => Left("An exception was thrown")
}

This will return a Right if the connector.makeCall() line returns true or a Left if that line returns false or an exception.

It's a bit of a contrived example but here's one way you'd use this - https://scastie.scala-lang.org/irmbBQ9ISeqgitRubC8q5Q