Support Microsoft Graph logon with self-signed certificates

[chhaugen]

MustMail looks awesome!

I have a suggestion for an improvement!
I have one minor concern, and that is looking after client secrets. As Azure only allows you to set a validity of only a couple of years for client secrects, certificates doesn't seam to have that issue. This would help take an aditional task off my calendar.

The SMTP2Graph prosject has this implemented and it works fine.
https://github.com/SMTP2Graph/SMTP2Graph

One can easily generate a self-sign certificate using Powershell and GIT Bash on Windows

$cert = New-SelfSignedCertificate `
  -Subject "CN=SMTP2GRAPH" `
  -CertStoreLocation "Cert:\CurrentUser\My" `
  -KeySpec KeyExchange `
  -KeyLength 2048 `
  -KeyExportPolicy Exportable `
  -HashAlgorithm sha256 `
  -NotAfter (Get-Date).AddYears(10)
  
Export-Certificate -Cert $cert -FilePath SMTP2GRAPH.cer

Export-PfxCertificate `
  -Cert $cert `
  -FilePath "SMTP2GRAPH.pfx" `
  -Password (ConvertTo-SecureString -String "Password123!" -Force -AsPlainText)

Git BASH:
openssl pkcs12 -in SMTP2GRAPH.pfx -nocerts -nodes -out key.pem

As you can see, Azure accepts it:

[bxdavies]

Hello,

Thank you for the suggestion. Currently, MustMail will automatically create a self-signed certificate if one is not provided.

I'll look at adding the option to use that certificate for Microsoft Graph authentication as well.

Once that feature is added, you'll be able to generate your own certificate using the command you suggested, provide it to MustMail, and use that certificate instead of a client secret for Microsoft Graph authentication.

In my experience, most enterprise applications tend to use client secrets rather than client certificates, although certificate-based authentication is becoming more common, so I'd like to support both.