Open draftcode opened 6 years ago
The original vgo prototype just read $HOME/.netrc. I'd rather do something like that than shell out to a whole separate program.
.netrc works for HTTP basic auth with unlimited lifetime credentials. But it doesn't work for other types, like:
Note that even "access denied" pages can have meta tags - go get does not require a 200 response, exactly for this kind of thing. So git.mycompany.com could serve the tags unauthenticated as one workaround.
Are there any more general "HTTP auth credential helpers" in the world besides git-credential-helper? How do other systems deal with this? If there's something standard to hook into (like .netrc) then that's better than designing our own.
If the access denied page contains the meta tag, it can be used as a prober. Let's say git.mycompany.com has an not-yet announced new product, collaborating with another company other-tech-company.com, and they host a Git repository at git.mycompany.com/ng-product/collab-other-tech-company. An attacker can probe if a repository exists by looking at the go-get's meta tag, and they can learn mycompany.com will have a business relationship other-tech-company.com to create a new product (and maybe benefit from this insider info).
As far as I know, there's no generic mechanism that majority of people use for storing and obtaining credentials through API. The closest thing I can think of is ssh-agent. Or if it's OS X, OS X Keychain.
It's only a prober if you check that the thing exists before serving the meta-tag.
$ curl 'https://rsc.io/asdgihopajdfklgadfglhifsdfj?go-get=1'
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<meta name="go-import" content="rsc.io/asdgihopajdfklgadfglhifsdfj git https://github.com/rsc/asdgihopajdfklgadfglhifsdfj">
<meta http-equiv="refresh" content="0; url=https://godoc.org/rsc.io/asdgihopajdfklgadfglhifsdfj">
</head>
<body>
Redirecting to docs at <a href="https://godoc.org/rsc.io/asdgihopajdfklgadfglhifsdfj">godoc.org/rsc.io/asdgihopajdfklgadfglhifsdfj</a>...
</body>
</html>
r$
Clearly we could use a better idea here but I'd like to have just one thing that's standard instead of inventing our own (that is, I want something like .netrc).
It's only a prober if you check that the thing exists before serving the meta-tag.
I cannot interpret this. The problem is that an attacker can use this to extract the repository existence by using this meta-tag. If the page checks if the repository exists and change the response, it can be used as a prober.
If the page checks if the repository exists and change the response, it can be used as a prober.
Then don't check, and don't change the response.
Are there any more general "HTTP auth credential helpers" in the world besides git-credential-helper?
https://docs.docker.com/engine/reference/commandline/login/#credentials-store
https://github.com/GoogleCloudPlatform/docker-credential-gcr
Then don't check, and don't change the response.
So the page should not do any auth, and should not contain meta tag? I thought you're suggesting to add a meta tag and in the next response you're saying not to add meta tag?
An example leakage: https://play.golang.org/p/rCYzVWQSQni
We want to avoid this. By adding a meta-tag to the response as rsc suggests, the repository existence is leaked.
@draftcode, I assumed what was meant as you should advertise it for all URLs, including /android/device/g000gle/foo-bar-not-exist , regardless of whether it actually exists.
I assumed what was meant as you should advertise it for all URLs, including /android/device/g000gle/foo-bar-not-exist , regardless of whether it actually exists.
Note that the third part in meta tag should be a git repository URL. This means, if a repository exists, the third part should be a valid Git repository path. In the example, I used example.com/android/device/google/marlin-kernel/foo/bar
as an example package path. The valid meta tag for this is <meta name="go-import" content="example.com git http://example.com/android/device/google/marlin-kernel">
, not <meta name="go-import" content="example.com git http://example.com/android/device/google/marlin-kernel/foo/bar">
. Because of this, I can tell whether a repository exists by adding paths that wouldn't exist. When I make a request, if meta tag's returned path is modified, it means the repository exists.
An example that for this: https://play.golang.org/p/OWb6zRUD02r
@draftcode I am saying that if you pick a trivial rule like "example.com/x/y/z/w redirects to the repo at git.example.com/x/y", then you can implement it with no Auth check and no repo validity check, so that it responds to any possible x/y/z/w with the same answer. Then there is no leakage. That was the point of my curl example above: there is no actual package at rsc.io/asdgihopajdfklgadfglhifsdfj but the curl still reads back meta tags for it.
If you need example.com/x/y/z/w to redirect to different git servers based on the exact values of x,y,z,w then that's more difficult of course and leakage is hard to avoid.
This is all just a suggested workaround. What I'd really like is to find out about some plausibly general (not git-specific, not docker-specific) semi-standard way to interact with credential helpers. Maybe none exists and we have to come up with something. But that would be my last choice.
If you need example.com/x/y/z/w to redirect to different git servers based on the exact values of x,y,z,w then that's more difficult of course and leakage is hard to avoid.
OK. We've considered that option when we investigated how GitHub deals with this, and found out that GitHub won't allow slashes in a repository name, so they can do what you've said. We cannot do that, so filed this bug.
What I'd really like is to find out about some plausibly general (not git-specific, not docker-specific) semi-standard way to interact with credential helpers. Maybe none exists and we have to come up with something. But that would be my last choice.
So far, I've shown what Git does for a similar problem. @bradfitz showed what Docker and GCP does for a similar problem (ADC now works only for service accounts, so it's a bit different). If there's a some standard way to get a cred, considering the size of these tools' community, there should be some implementation of that, but it seems there's no such thing. In fact, Docker created a credential helper mechanism following what Git did. From these, such standard, if exists, is something that Git and Docker communities at least are not aware of and are not using. @rsc, @bradfitz, and I are also not aware of such generic way that would be called as "semi-standard", it seems.
Given that there doesn't seem to be an agreed-upon standard, I guess the next step is for someone to propose a design that Go should use. I looked at git credential helpers but stopped looking when I saw bash snippets.
Questions on the requirements:
My impression is that @rsc strongly prefers using a file instead of executing a command and using stdin/stdout. Is this a hard requirement?
He objected to bash snippets. It is possible (I do not know) that executing a binary rather than a shell might sit better with him.
If it were indeed command execution (a la EDITOR
), then e.g. those of us who use 1password could use their command line support. I think macOS keychain has similar support.
Command-line execution seems necessary, since you want to lock things down and give cmd/go access to just one password, not your whole password set. Josh, what did you have in mind? Want to propose a starting point design?
It would be great if we could achieve the stated above goal ("Make go get git.mycompany.com/private-repo
work, where https://git.mycompany.com/private-repo
requires authentication") without forcing the users to perform custom modifications to their ~/.netrc
or ~/.gitconfig
files (or installing extra binaries) - at least in the (I believe) common cases of GitHub [Enterprise] with SSH authentication (from the ssh agent).
Assuming the server returns a meta tag such as <meta name="go-import" content="git.mycompany.com/org/repo git https://git.mycompany.com/org/repo.git">
, could the go
tool try the following:
git ls-remote -q https://git.mycompany.com/org/repo.git
first (as now)Username for 'https://git.mycompany.com':
, try next the command with the corresponding ssh URL: git ls-remote -q ssh://git@git.mycompany.com/org/repo.git
- and if it works, remember / cache that protocol for other git operations with the server (at least, within the same go
invocation). (The git
user must be standard for GitHub as it is indicated on https://help.github.com/articles/testing-your-ssh-connection/ and https://help.github.com/enterprise/2.14/user/articles/testing-your-ssh-connection/). This "retrial" step can be limited to the cases where server replies with Server: Github.com
HTTP header ([1], [2]).I believe this would make possible to use git with the SSH auth without having everyone to add the insteadOf
stanzas in ~/.gitconfig
on every server / VM or putting passwords in ~/.netrc
etc. (To avoid this, we currently have to use a redirect server on an equivalent of go.mycompany.com
that sends back <meta name="go-import" content="git.mycompany.com/org/repo git ssh://git@git.mycompany.com/org/repo">
- but it would be so nice to be able to use the "natural" git.mycompany.com/org/repo
as imports / package names instead of go.mycompany.com
and forcing everyone to learn and use the git.mycompany.com
=> go.mycompany.com
replacement!) Having all Go users in the company to install an additional binary to bridge go
and auth secrets would IMO be even more cumbersome (and the security team will likely consider it as yet another thing to worry about...).
I think it is an incredible strength of the Go tool that you can install and use it "right out of the box" - would love to see that feature and stellar user experience preserved and extended! 😄
[1] https://go-review.googlesource.com/c/go/+/33171 (abandoned; issue https://golang.org/issue/17898) [2] Russ's comment - https://github.com/golang/go/issues/24076#issuecomment-377562501
Assuming the server returns a meta tag
@dmitris This proposal is for the servers that cannot return meta tags without an auth (see https://github.com/golang/go/issues/26232#issuecomment-412958321). It seems to me that your problem is not related to this.
@bcmills we should probably make this a Go 1.13 early.
- OAuth2 access tokens usually have a limited lifetime, and it needs to be issued dynamically. Because of this, this cannot be in a static file.
Heroku takes an interesting approach to that: their CLI obtains a fresh OAuth2 token and writes it to the user's .netrc
file.
@dmitris, if the user is able to contact the private HTTPS server, and the server knows that the repo is also private, why couldn't it provide an ssh://
URL in the <meta>
tag (instead of an https://
URL) itself?
@bcmills yes that works. Actually the modern GHE provides the Go meta tags "natively" so we were able to switch to git.xyzcompany.com
imports and shut down the go.xyzcompany.com
redirect server. My only gripe now is that go
seems to prefer https://
git URLs + "personal access tokens" (as in https://help.github.com/articles/creating-a-personal-access-token-for-the-command-line/) while the standard at our company is the SSH authentication and git@git.xyzcompany.com
URLs, so everyone has to add the insteadOf
incantation in ~/.gitconfig
in every environment / VM. To make clear - I'm not blaming Go at all, GitHub itself says cloning with HTTPs is recommended on https://help.github.com/articles/which-remote-url-should-i-use/ - so it is a reasonable pick. I still wish go
would try both and use whichever one works so that we could run go install
or go get
without stumbling on the missing insteadOf
config...
I have a tangential question: is it possible to pass to the go
tool a client TLS certificate + key + CAcert (in environment variables or otherwise)? It could be useful in environments that take Zero Trust Networking seriously and where go
tool needs to talk to the other side (the replace
targets) that lives in a public cloud using mutual TLS for authN/Z. (This is hypothetical - we haven't yet had that requirement specifically for go, but mTLS is standard/required for communicating with the clouds)
SSH vs. HTTPS for GitHub in particular is tracked in #26134.
I'm not sure about mTLS — please file that separately.
Here is my proposed design for Go 1.13.
A new environment variable, GOAUTH
, will contain a list of authenticator commands to invoke: each command is a space-separated argument list, and the commands themselves are separated by semicolons.
The go
command will maintain, in memory, a cache of credentials produced by GOAUTH
invocations, and use them for both go-import
resolution and the HTTPS module proxy protocol.
Before the first HTTPS fetch, the go
command will invoke each GOAUTH
command in the list with no additional arguments and no input. The GOAUTH
command may reply with zero or more credentials to cache, written to stdout
in this format:
https://
and ending at a complete path element.For each URL to be fetched, the go
command will check the credential cache and apply the first matching credential from the command that appears earliest in the list, appending the corresponding headers to its own request headers (if any).
If the server responds with any 4xx code and the response body does not satisfy the request (for example, by including a valid <meta name="go-import">
tag), the go
command will invoke the GOAUTH
commands again, this time with the URL as an additional command-line argument. The go
command will also write the following to the programs' stdin
:
net/http
package(Note that, at least for HTTP 1.1, the contents written to stdin
can be parsed verbatim as an HTTP HEAD
response.)
Each GOAUTH
command may reply with credentials as before, and those credentials take precedence over any previous credentials from that command for that prefix. (A non-empty list of prefixes followed by an empty list of request headers removes the previous credentials.) If none of the credentials in the replies match the request, the go
command fails the fetch.
The go
command will then retry the fetch with the updated credential for the URL. If the server responds with an error again, the fetch fails: a URL-specific GOAUTH
will only be attempted once per fetch.
The go
command will recognize three builtin GOAUTH
commands: off
, netrc
, and git
. The netrc
implementation will be equivalent to the go
command's existing .netrc
file support. The git
implementation will use git credential fill
. The default value of GOAUTH
(if not set in the environment) will be netrc
, preserving the credential behavior from Go 1.12.
This approach provides very wide latitude for the authentication mechanism, while keeping the protocol close to HTTP itself. (The implementation for git credential
is straightforward, and .netrc
and cookies.txt
should be similar.)
The initial calls to the GOAUTH
programs reduce overhead from repeated command invocations (and latency from initial credential misses), while the secondary calls allow the programs to respond intelligently to authentication hints from the server (such as WWW-Authenticate
types and realms).
Command:
$GOAUTH https://github.com/bcmills/private-repo
Input to GOAUTH
:
HTTP/1.1 404 Not Found
Cache-Control: no-cache
Content-Security-Policy: default-src 'none'; base-uri 'self'; connect-src 'self'; form-action 'self'; img-src 'self' data:; script-src 'self'; style-src 'unsafe-inline'
Content-Type: text/html; charset=utf-8
Date: Wed, 06 Feb 2019 22:47:12 GMT
Expect-Ct: max-age=2592000, report-uri="https://api.github.com/_private/browser/errors"
Referrer-Policy: origin-when-cross-origin, strict-origin-when-cross-origin
Server: GitHub.com
Set-Cookie: has_recent_activity=1; path=/; expires=Wed, 06 Feb 2019 23:47:12 -0000
Set-Cookie: _gh_sess=ZWdxekI4RlFHbS82MEl5djZwcWNrRHJqdzhUNDlpTFM4aVFOa2E2TDRRTWFuZkhJenBDdmVYc24rYXBFZXJOTHN3VGdTZnc2RGVpYndmdTJCVFVTeE4zaTRkbHR0ZHYrODJLQTdqR1llaFQrVklQSk9YSWw2b3lROWxleENtL0ItLUJ2MGs1TnhuTnVPMTBpdXRIcUFSVmc9PQ%3D%3D--47220df4045034db9d8ce85c771e0d20341b29c0; path=/; secure; HttpOnly
Status: 404 Not Found
Strict-Transport-Security: max-age=31536000; includeSubdomains; preload
Vary: X-PJAX
X-Content-Type-Options: nosniff
X-Frame-Options: deny
X-Github-Request-Id: CE63:55B5:2AF684:48FB29:5C5B63F0
X-Request-Id: 8c810f80-9be4-48d9-b8c4-9a31b56aa312
X-Xss-Protection: 1; mode=block
Output from GOAUTH
:
https://github.com
Authorization: Basic YWxhZGRpbjpvcGVuc2VzYW1l
(Note: the credential above is aladdin:opensesame
, the standard example username and password for HTTPS auth protocols. Please be careful not to paste real credentials!)
Change https://golang.org/cl/161698 mentions this issue: cmd/go/internal/web2: make netrc parsing more robust
Change https://golang.org/cl/161666 mentions this issue: cmd/auth/authtest: add a manual-test harness for GOAUTH implementations
Change https://golang.org/cl/161667 mentions this issue: cmd/auth/gitauth: add a reference GOAUTH implementation using 'git credential fill'
Change https://golang.org/cl/161668 mentions this issue: cmd/auth/netrcauth: add a reference GOAUTH implementation using .netrc files
Change https://golang.org/cl/161669 mentions this issue: cmd/auth/cookieauth: add a GOAUTH implementation that reads from a cookiefile
I talked with @bcmills about his proposed solution, and it seems worth trying. Does anyone object to accepting this?
@bcmills @rsc - looks great, just a couple of questions:
.netrc
file or a credential helper?GOAUTH
for 1.13 netrc;git
? For those people (and selfishly I count myself amongst them) who have a git credential helper set, this will save setting another global environment variable. And in any case I'm guessing using a git
credential helper is the direction in which we want to be pushing people?Many people who have hit auth-related issues thus far use git over ssh. Am I right in concluding that for these people their lot will not improve […]?
The main git-over-ssh use-case is #26134, which we should address separately.
In general, if a repo cannot be accessed via HTTPS at all, then its <meta name="go-import" […]>
tag should provide an appropriate ssh://
URL.
We can probably provide some sort of automatic fallback for the hard-coded hosting services, but in general if we receive an HTTPS URL we don't know what username to try for ssh
, even if we could infer the rest of the path.
We may want to allow the go-import
tag to list multiple alternative URLs (for example, on https://
and one ssh://
), but if we do that we'll have to be very careful not to break the existing parsers with it.
Is there any harm in making the default value of
GOAUTH
for [1.13]netrc;git
?
git credential fill
is aggressively interactive, so that could jam up folks' CI configurations and generally mess with scripting. In contrast, we can look for a .netrc
file without any user interaction whatsoever.
I'd like to keep the default non-interactive if we can.
Thanks, all makes sense now.
In general, if a repo cannot be accessed via HTTPS at all, then its
<meta name="go-import" […]>
tag should provide an appropriatessh://
URL.
Right so in the main (?) scenario, we're assuming that the initial ?go-get=1
request will be unauthenticated.
Is it documented anywhere that a go-import
meta tag can supply an ssh://
URL?
https://tip.golang.org/cmd/go/#hdr-Remote_import_paths
Or are you saying this is how that use case will be solved in future?
git credential fill
is aggressively interactive
Presumably the interactive mode is some sort of fallback; I'm guessing from your response it's not possible to tell git not to use that fallback.
Presumably the interactive mode is some sort of fallback; I'm guessing from your response it's not possible to tell git not to use that fallback.
Correct. To be precise, if $GIT_ASKPASS
or $SSH_ASKPASS
fails to return a credential, git credential fill
will look for (and open) /dev/tty
and issue a password prompt itself.
That's the right thing to do if the user actually wants to type it a password (that is, if the go
command itself is invoked interactively), but totally wrong in a CI or IDE context.
Is it documented anywhere that a
go-import
meta tag can supply anssh://
URL?
I don't think we give an example of it, but if that doesn't work today, then I will make it work. 😤
The
GOAUTH
command may reply with zero or more credentials to cache, written tostdout
in this format:
I want to check if I understand this correctly. GOAUTH
may reply multiple sets of the credentials. The response format is:
RESPONSE ::= CREDENTIAL_SET*
CREDENTIAL_SET ::= (URL NEWLINE)+ NEWLINE (HEADER NEWLINE)* NEWLINE
URL ::= /* URL that starts with "https://" */
NEWLINE ::= '\n'
HEADER ::= /* HTTP header */
Right so in the main (?) scenario, we're assuming that the initial
?go-get=1
request will be unauthenticated.
FYI, gitlab need authentication for private repos in nested sub-group. So I think the initial ?go-get=1
request need to support authentication too.
@myitcv
Right so in the main (?) scenario, we're assuming that the initial ?go-get=1 request will be unauthenticated.
Not necessarily. The protocol in this proposal would apply to both the initial ?go-get=1
fetch, any subsequent requests that use the mod
protocol, and any HTTPS traffic to the configured GOPROXY
server.
(When using VCS tools for direct fetches, it's still up to those individual tools to decide how to authenticate their own internal HTTPS traffic, if any.)
Aren't we reinventing the wheel here? I not sure which other VCS's are supported/used by go get
, but in the case of git
, authentication is built in for both HTTP and SSH transports. For HTTP there's gitcredentials and for SSH there's ssh_config(5). git
also supports other protocols but I think it's safe to say that they are outside scope. I'm sure other VCS's have similar approaches.
If we leave authentication to the VCS, the go tool chain only needs to instruct the VCS which url to use and make this configurable by the user.
Make go consult a config file before downloading a dependency. The file should contain a mapping between import paths and the url passed to the VCS. E.g:
example.com/foo/bar git@example.com:foo/bar.git
As a side effect this also allows uses of simple proxies.
@palsivertsen, the go
tool does not make every HTTPS request through a VCS tool. This proposal is specifically for the requests that are not made through a VCS.
Note that git credential fill
is one of the supported credential sources under this proposal: if you want to use it, you will be able to set GOAUTH=git
and won't need to write any additional configuration files.
Change https://golang.org/cl/170581 mentions this issue: vcs-test/vcweb: add a handler that requires HTTPS Basic Auth
@bcmills Which calls does the go
tool need to make calls outside a VCS tool?
Maybe this is the wrong issue, but I'm trying to find a solution for when the following is true for a dependency:
I came here from #29094 which is a symptom of the above case. There are a lot of similar issues like this and so far I've found only one workaround which involves renaming the dependency and tricking the go
tool into using ssh.
Which calls does the
go
tool need to make calls outside a VCS tool?
It makes https://[…]?go-get=1
requests to resolve paths to repos (using go-import
meta tags), and if the go-import
tag indicates mod
then it uses HTTPS to fetch the resulting modules (using the protocol described in https://tip.golang.org/cmd/go/#hdr-Module_proxy_protocol).
I'm trying to find a solution for when the following is true for a dependency:
- Requires authentication
- Host will deny any existence of resource unless request is authenticated
- Authenticating HTTP requests is not an option (2FA / weak passwords)
You only get to pick two of those: “requires authentication” and “authenticating […] is not an option” are mutually exclusive.
But note that the protocol described in https://github.com/golang/go/issues/26232#issuecomment-461525141 allows the GOAUTH
plugin to do whatever it needs to do to authenticate — including interacting with the user to obtain 2FA credentials — as long as it can encode the result as a URL prefix and a set of HTTP request headers.
NOTE: The accepted proposal is https://github.com/golang/go/issues/26232#issuecomment-461525141.
Problem
The custom import path mechanism (
?go-get=1
and meta tag) works for public URLs, but it doesn't work for auth required URLs. This is because when go-get fetches the URL with?go-get=1
, it uses net/http.DefaultClient, and it doesn't know the credentials it needs to access the URL. A user cannot rungo get
against private source code hosting service because of this.Goal
Make
go get git.mycompany.com/private-repo
work, where https://git.mycompany.com/private-repo requires authentication.Idea 1 (credential helper)
Introduce a credential helper mechanism like git-credential-helpers. A user specifies a path to a binary via
GOGET_CREDENTIAL_HELPER
andgo get
executes that with the import path as an argument. The credential helper binary returns HTTP headers (like "Authorization: Basic blah\n", andgo get
adds these headers when it tries to fetchgo-get=1
URLs.Idea 2 (go-get helper)
Introduce a custom source code fetching mechanism. When
go get
needs to fetch the source code for the import pathgit.mycompany.com/private-repo
, it looks for the binarygo-get-git.mycompany.com
based on the host name of the import path. When such binary exists in $PATH, it executes that binary with the import path and a destination in $GOPATH (for example,go-get-git.mycompany.com git.mycompany.com/private-repo $GOPATH/src/git.mycompany.com/private-repo
). The binary is responsible for fetching the source code to the specified $GOPATH location.go get
work with VCSs other than git/hg/svn/bzr.go get -f
orgo get -insecure
.