Reading two Repos in Azure Build pipeline
I also use the classic editor, and I have implemented this for our builds. My use case was that I have a set of common set of build/release scripts stored in their own repository, and I want the ability to bring them into the application builds that I am executing.

I created a custom Task Group with an Inline PowerShell script to do this:

# Reference: https://blog.rsuter.com/script-to-clone-all-git-repositories-from-your-vsts-collection/
Write-Host "Cloning MyRepo from Azure DevOps..."

$sourcesDir = $env:SYSTEM_DEFAULTWORKINGDIRECTORY
Write-Host "Source directory: $sourcesDir"
$repoDir = Join-Path -Path "$sourcesDir" -ChildPath "MyRepo"
Write-Host "Target directory: $repoDir"

$url = "https://dev.azure.com/my_org/my_team_project/_git/MyRepo"

# Since using PAT, don't need real username, just non-empty username. Use "x".
$username = "x"
$pat = $env:PAT # passed into inline script as environment variable
$credentials = ("{0}:{1}" -f  $username, $pat)
$urlWithCreds = $url -Replace "://", ("://{0}@" -f $credentials)
Write-Host "Clone URL: $urlWithCreds"

git --version
git clone --progress $urlWithCreds
Set-Location "$repoDir"
git checkout master
git log -1 # show the latest commit


You will have to create a PAT with code permissions and pass it into the script as an environment variable. This task will clone the repository to a directory of the same name within your existing repo.

Putting it in a task group allows me to manage it in one place, and then all my more complicated build scripts can be under version control.

There is an active feature request for the capability to source from multiple repos. It looks like it is in the roadmap: https://developercommunity.visualstudio.com/idea/365522/allow-tfs-build-to-depend-on-multiple-repositories.html