Analyzing Exchange Online scripts

Since the original announcement on deprecation of Basic Authentication, organizations had time to analyze their environment which may include Exchange-related procedures and tools. These usually also contain scripts or commands, which depend on the Exchange Online Management module. A previous blog on its history and how version 2 of this module lends itself for unattended operation with certificate-based modern authentication support can be found here.

The initial release of the Exchange Online Management v2 – or EXOv2 – module offered a an additional small set of cmdlets which utilized REST-based services. Apart from the functional discrepancies, such as having to specify a property set to indicate which properties to return, the big advantage of these added commands was that they did not depend on the Windows Remote Management (WinRM) client using Basic Authentication for token exchange. Disabling Basic Authentication on WinRM client lead to messages such as:

Connecting to remote server failed with the following error message : The WinRM client cannot process the request. Basic authentication is currently disabled in the client configuration.

This dependency makes it challenging for organizations to turn off Basic Authentication altogether, or lead to problems when they did. Fast forward to the present, where the Exchange Online Management module in its current release is offering nearly all Exchange cmdlets in REST-based form, with full functional parity.

While I expect Microsoft to reach full command parity before they flick the Basic Authentication switch to off, there are also other use cases for which analyzing scripts might be helpful:

  • Ths initial purpose was identifying commands which require RPS (Remote PowerShell), and thus thus require WinRM Basic Authentication enabled. Because the Exchange Team did an amazing job in catching up in the recent months, only few Exchange Online cmdlets are still lacking REST support in my tenant at this moment, e.g. New-ApplicationAccessPolicy. But then again, your mileage may vary.
  • New Exchange Online commands may not receive immediate REST support.
  • Organizations might want to cross-reference commands with scripts.
  • Identifying Exchange Online commands and parameters in scripts helps in determining the minimum set of permissions required to run the script.

To analyze and report on Exchange Online scripts, I created a simple script Analyze-ExoScript.ps1. This script, which is available on GitHub here, does the following:

  • Connect to Exchange Online using RPS and inventory the commands available. Note that this requires the UseRPSSession switch when connecting, which is only available per 2.0.6-Preview3 of the module. If your organization only runs GA versions of the module, this script cannot be used.
  • Connect to Exchange Online using REST and inventory the commands available. It will re-use the account used for authenticating the RPS session, which should prevent receiving another authentication dialog or MFA challenge.
  • Cache cmdlet information in an external file to prevent having to connect to Exchange Online for every run. The file is named EXO-CmdletInfo.xml and will be stored in the same folder as the script.
  • Process the script and report on the Exchange-related commands used.

Calling Analyze-ExoScript is straightforward:

.\Analyze-ExoScript.ps1 [-File <FileName[]>] [-ShowAll] [-Refresh]


  • Filename is the name of one or more files which you cant to analyze. Note that the script accepted pipeline output, so you can also feed it filenames using Get-ChildItem for example.
  • The ShowAll switch tells the script to output all found commands, not only the Exchange ones.
  • The switch Refresh tells the script to ignore saved command information, trigger reconnecting to Exchange Online in order to refresh the command sets.

When asked to authenticate, make sure your role has the necessary Exchange-related permissions as that will determine the Exchange Online cmdlets available to you, and consequently also the commands which Analyze-ExoScript will recognize in scripts to process.

For example, to process a script Fix-MailboxFolders.ps1, use:

.\Analyze-ExoScript.ps1 -File .\Fix-MailboxFolders.ps1

The script can accept files via the pipeline. For example, to process multiple scripts use something like:

Get-ChildItem -Path C:\temp*.ps1 | Analyze-ExoScript.ps1

The output consists of objects, which allow for further filtering:

The returned properties are:

  • Command is the Exchange Online command identified
  • Type will tell you if the command supports REST, if it requires RPS, or it requires RPS but can be refactored (MAP) to a REST-based command, and which one that would be.
  • Parameters are the parameters used together with the command. This includes common parameters, which might be less usable for role assignment purposes.
  • File and Line are the file containing the command and on which line it is located.

To analyze code, I leveraged PowerShell feature called Abstract Syntax Tree, which was an interesting exploration in itself. PowerShell AST can be used to decompose PowerShell code into tokens. This is way better than simply looking for strings, and does away with having to interpret code yourself to see if something is a command, comment or just some string. AST allows for analysis of these tokens, in this case filtering on commands which are related to Exchange Online. If you want to get started on AST, check out this article, or plunge in the PowerShell SDK straightaway.

Final Words
When every Exchange Online command discovered is found to be offering REST support, you can turn off Basic Authentication on the client, for example through GPO or by reconfiguring WinRM:

winrm set winrm/config/client/auth @{Basic="false"}

Only thing you might need to refactor is if and how the script connects to Exchange Online, as Basic Authentication allowed for connecting to Exchange Online using (stored) credentials for example. Examples on how to use more secure Modern Authentication-based methods to connect can be found in an earlier article here.

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