I encounter the following error when attempting to add a certificate, it's filename cert.pem, for an Azure AD app that I am integrating:
Failed to add certificate. Error detail: Upload a certificate (public key) with one of the following file types: .cer, .pem, .crt
I am sure that even though the file type is correct (.pem) the structure and content of the file is incorrect, but I don't know how to fix it.
As you said, the content of the file is incorrect. You could create a certificate for testing purposes using PowerShell with New-SelfSignedCertificate. Try to refer to here. Make sure you open PowerShell as an admin account.
$pwd = "<password>"
$currentDate = Get-Date
$endDate = $currentDate.AddYears(10) #10 years is nice and long
$thumb = (New-SelfSignedCertificate -DnsName "techmikael.com" -CertStoreLocation "cert:\LocalMachine\My" -KeyExportPolicy Exportable -Provider "Microsoft Enhanced RSA and AES Cryptographic Provider" -NotAfter $endDate).Thumbprint
$pwd = ConvertTo-SecureString -String $pwd -Force -AsPlainText
Export-PfxCertificate -cert "cert:\localmachine\my\$thumb" -FilePath .\techmikael.pfx -Password $pwd
$path = (Get-Item -Path ".\").FullName
$cert = New-Object System.Security.Cryptography.X509Certificates.X509Certificate("$path\techmikael.pfx", $pwd)
$keyValue = [System.Convert]::ToBase64String($cert.GetRawCertData())