I'm trying to create a build pipeline in azure devops for .net core app with code from other git repository and providing user name and password. But I ended up with below error. Help me out
fatal: Authentication failed for git url
##[error]Git fetch failed with exit code: 128
Attached the error for the reference along with pipeline configuration 
Disclamer: There is not enough information in your question to know if this advice apply. It only apply if you want to fetch from another Azure DevOps repository.
If you need to fetch from another Azure DevOps repository, you will have to set an header:
git -c http.extraheader="AUTHORIZATION: bearer %YOUR_TOKEN%" fetch --tags --prune --progress --no-recurse-submodules origin
If you want to fetch lfs file:
git -c http.https://taliance.visualstudio.com.extraheader="AUTHORIZATION: bearer %YOUR_TOKEN%" lfs fetch origin %Build_SourceVersion%
Note: %YOUR_TOKEN% could be replaces by %System_AccessToken% if you want to fetch from a git repository inside the same Azure DevOps project.
You could find more information in this answer: https://stackoverflow.com/a/53182981/717372
It might be an old post, but as I was struggling with that one for (way too) long time I can provide you what helped me:
There happened to be (another?) extraheader in my global configuration settings which seemed to be obsolete or false. So I unset this variable which resolved the issue.
/usr/bin/git config --global --unset http.extraheader
You can check your settings beforehand using:
git config --global --list
Azure DevOps error 'Git fetch failed with exit code 128' during build pipeline of other git Repository
According to the error message, fatal: Authentication failed for git url . This is indeed a issue from credentials.
When we create the service connections for the other git, there is no Verify option provided here, so we could sure whether the certification or service connection we provide are correct.
First, we need make sure we have checked the checkbox Grant access permission to all pipelines when we create the service connection:
Second, we need to verify the Username and Password/Token are correct. Since there is no such verify option, we could use git clone command with Username and Password/Token in the command line task:
git clone https://username:password@xxx.org/username/repository.git
Or
git clone https://PAT@xxx.org/username/repository.git
You could check this thread for some more details.