threads / discuss / 54398

How to Verify the Git Credentials supplied by the User

Subject: How to Verify the Git Credentials supplied by the User

## tl;dr

4 messages between Oct 12, 2020 and Oct 13, 2020.

replies: 3people: 2as markdown or json

Deepak Patankar· Oct 12, 2020, 13:50 UTC · lore
Hello!!

I am writing an application in which we will support git integration. The user will provide us with his/her git credentials so that we can push some files on his git. The git credentials which user will supply can be

HTTP (Username and Password/ Kerberos) SSH

Before saving the user credentials I want to validate that the credentials entered is valid.

The user might be using GithHub/BitBucket/GitLab. I am trying to find some git command which I can use to validate the credentials. Can you please point me to some command/logic which I can try?

What I have tried? I tried git ls-remote command, but it requires the repo name/url. In one of our use case, the user won't specify the repository name beforehand. Because of which I am not able to use this command.

Thanks Deepak Patankar

Junio C Hamano· Oct 12, 2020, 17:46 UTC · re: Deepak Patankar · lore

Re: How to Verify the Git Credentials supplied by the User

Deepak Patankar <patankardeepak04@gmail.com> writes:
Show 10 quoted lines
> I am writing an application in which we will support git integration.
> The user will provide us with his/her git credentials so that we can
> push some files on his git. The git credentials which user will supply
> can be
>
> HTTP (Username and Password/ Kerberos)
> SSH
>
> Before saving the user credentials I want to validate that the
> credentials entered is valid.

It obviously depends on the remote side, but a relatively safe thing to try is to run things like "ls-remote" or "push --dry-run" that will not cause any actual damage against the remote, and see if your authentication fail.

But you might be asking a XY question. I would expect that any reasonable application that manages authentication material for the user and drives "git fetch" and "git push" would act as a credential helper and uses the credential protocol to talk to Git, so it will learn an authentication failure upon the first use, at which point it has the chance to drop the authentication material it obtained earlier and ask the user for the corrected one---there is no need for the application to see if the authentication material is correct before the user does anything else.

Show 8 quoted lines
> The user might be using GithHub/BitBucket/GitLab. I am trying to find
> some git command which I can use to validate the credentials. Can you
> please point me to some command/logic which I can try?
>
> What I have tried?
> I tried git ls-remote command, but it requires the repo name/url. In
> one of our use case, the user won't specify the repository name
> beforehand. Because of which I am not able to use this command.

This assumes there always is a single authentication material regardless of the URL, which is probably not a good security posture to encourage the users to adopt.

Deepak Patankar· Oct 13, 2020, 05:24 UTC · lore

Re: How to Verify the Git Credentials supplied by the User

Hey Junio,
Thanks a lot for the help.
On Mon, 12 Oct 2020 at 23:16, Junio C Hamano <gitster@pobox.com> wrote:
Show 29 quoted lines
>
> Deepak Patankar <patankardeepak04@gmail.com> writes:
>
> > I am writing an application in which we will support git integration.
> > The user will provide us with his/her git credentials so that we can
> > push some files on his git. The git credentials which user will supply
> > can be
> >
> > HTTP (Username and Password/ Kerberos)
> > SSH
> >
> > Before saving the user credentials I want to validate that the
> > credentials entered is valid.
>
> It obviously depends on the remote side, but a relatively safe thing
> to try is to run things like "ls-remote" or "push --dry-run" that
> will not cause any actual damage against the remote, and see if your
> authentication fail.
>
> But you might be asking a XY question.  I would expect that any
> reasonable application that manages authentication material for the
> user and drives "git fetch" and "git push" would act as a credential
> helper and uses the credential protocol to talk to Git, so it will
> learn an authentication failure upon the first use, at which point
> it has the chance to drop the authentication material it obtained
> earlier and ask the user for the corrected one---there is no need
> for the application to see if the authentication material is correct
> before the user does anything else.
>

My previous email was confusing. I will be doing the authentication check the way you described above i.e. it will be done only once and I won't do it again and again before each operation.

I can use the "ls-remote", "push --dry-run" command you suggested, but I have a use case which I don't know how to solve. The above commands require a repository. In our application, the user can give the following details

Git Details:
   Account URL:  https://github.com/OpenPrinting
   UserName: deepakpatankar
   password: ***********

In this case, we don't know the repo name. At this step, I just know the account and the credentials of the user, later on the user will provide me with the repo name to which he wants to sync his file.

Since I don't know the repository, I cannot do "git fetch" or "git push --dry-run". Can I check this credentials with some logic or git commands?

Thanks Deepak Patankar

On Tue, 13 Oct 2020 at 10:25, Deepak Patankar <patankardeepak04@gmail.com> wrote:

Show 79 quoted lines
>
> Hey Junio,
>
> Thanks a lot for the help.
>
> On Mon, 12 Oct 2020 at 23:16, Junio C Hamano <gitster@pobox.com> wrote:
> >
> > Deepak Patankar <patankardeepak04@gmail.com> writes:
> >
> > > I am writing an application in which we will support git integration.
> > > The user will provide us with his/her git credentials so that we can
> > > push some files on his git. The git credentials which user will supply
> > > can be
> > >
> > > HTTP (Username and Password/ Kerberos)
> > > SSH
> > >
> > > Before saving the user credentials I want to validate that the
> > > credentials entered is valid.
> >
> > It obviously depends on the remote side, but a relatively safe thing
> > to try is to run things like "ls-remote" or "push --dry-run" that
> > will not cause any actual damage against the remote, and see if your
> > authentication fail.
> >
> > But you might be asking a XY question.  I would expect that any
> > reasonable application that manages authentication material for the
> > user and drives "git fetch" and "git push" would act as a credential
> > helper and uses the credential protocol to talk to Git, so it will
> > learn an authentication failure upon the first use, at which point
> > it has the chance to drop the authentication material it obtained
> > earlier and ask the user for the corrected one---there is no need
> > for the application to see if the authentication material is correct
> > before the user does anything else.
> >
>
> My previous email was confusing. I will be doing the authentication
> check the way you described above
> i.e. it will be done only once and I won't do it again and again
> before each operation.
>
>
> I can use the "ls-remote", "push --dry-run" command you suggested, but
> I have a use case which I don't know how to solve.
> The above commands require a repository. In our application, the user
> can give the following details
>
> Git Details:
>    Account URL:  https://github.com/OpenPrinting
>    UserName: deepakpatankar
>    password: ***********
>
> In this case, we don't know the repo name. At this step, I just know
> the account and the credentials of the user, later on
> the user will provide me with the repo name to which he wants to sync his file.
>
> Since I don't know the repository, I cannot do "git fetch" or "git
> push --dry-run". Can I check this credentials with some
> logic or git commands?
>
>
> Thanks
> Deepak Patankar
>
>
>
> >
> > > The user might be using GithHub/BitBucket/GitLab. I am trying to find
> > > some git command which I can use to validate the credentials. Can you
> > > please point me to some command/logic which I can try?
> > >
> > > What I have tried?
> > > I tried git ls-remote command, but it requires the repo name/url. In
> > > one of our use case, the user won't specify the repository name
> > > beforehand. Because of which I am not able to use this command.
> >
> > This assumes there always is a single authentication material
> > regardless of the URL, which is probably not a good security posture
> > to encourage the users to adopt.
Junio C Hamano· Oct 13, 2020, 05:32 UTC · re: Deepak Patankar · lore

Re: How to Verify the Git Credentials supplied by the User

Deepak Patankar <patankardeepak04@gmail.com> writes:
Show 17 quoted lines
> I can use the "ls-remote", "push --dry-run" command you suggested, but
> I have a use case which I don't know how to solve.
> The above commands require a repository. In our application, the user
> can give the following details
>
> Git Details:
>    Account URL:  https://github.com/OpenPrinting
>    UserName: deepakpatankar
>    password: ***********
>
> In this case, we don't know the repo name. At this step, I just know
> the account and the credentials of the user, later on
> the user will provide me with the repo name to which he wants to sync his file.
>
> Since I don't know the repository, I cannot do "git fetch" or "git
> push --dry-run". Can I check this credentials with some
> logic or git commands?

You'd have to go outside Git, as our transport layer is only about talking with existing repositories. You cannot even create a new repository using Git native methods.

You may need to find a method that works with GitHub account (note that I am not even using the word repository here, instead saying "account") and such a method would likely have to involve GitHub specific API, but it probably would not work with other hosting providers.

I also would imagine that even at GitHub, one may want to use different authentication info depending on which repository one accesses, so the "there is a single User with a password at this hosting site" data model might turn out to be insufficient, but that is outside the scope of Git proper.

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