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cmd/go: define HTTP authentication extension mechanism #26232

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draftcode opened this issue Jul 5, 2018 · 82 comments
Open

cmd/go: define HTTP authentication extension mechanism #26232

draftcode opened this issue Jul 5, 2018 · 82 comments
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early-in-cycle A change that should be done early in the 3 month dev cycle. Proposal Proposal-Accepted
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@draftcode
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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 run go 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 and go get executes that with the import path as an argument. The credential helper binary returns HTTP headers (like "Authorization: Basic blah\n", and go get adds these headers when it tries to fetch go-get=1 URLs.

  • PRO: Straightforward solution to the problem description.
  • CON: Supporting multiple credential helpers becomes complicated. Git's credential helper mechanism supports multiple credential helper, and Git runs each in order. This sometimes makes an unexpected behavior that is hard to debug.

Idea 2 (go-get helper)

Introduce a custom source code fetching mechanism. When go get needs to fetch the source code for the import path git.mycompany.com/private-repo, it looks for the binary go-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.

  • PRO: As a side effect, this make go get work with VCSs other than git/hg/svn/bzr.
  • CON: I'm not sure how this works with go get -f or go get -insecure.
@gopherbot gopherbot added this to the Proposal milestone Jul 5, 2018
@draftcode
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Related issues: #16315 #11032

@rsc
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rsc commented Jul 5, 2018

The original vgo prototype just read $HOME/.netrc. I'd rather do something like that than shell out to a whole separate program.

@draftcode
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.netrc works for HTTP basic auth with unlimited lifetime credentials. But it doesn't work for other types, like:

  • OAuth2 access tokens. 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.
  • Cookie based auth. netrc as a format is not a format that represent an HTTP cookie. Alternatively, Netscape's cookie file format (the same format as .gitcookies) can be used. This cannot support dynamically generated credentials as well. We actually have Git repositories that are behind dynamically generated cookie-based auth at Google (BeyondCorp at Google: https://cloud.google.com/beyondcorp/).

@rsc
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rsc commented Jul 9, 2018

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.

@draftcode
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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.

@rsc
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rsc commented Jul 23, 2018

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$ 

@rsc
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rsc commented Jul 23, 2018

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).

@draftcode
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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.

@rsc
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rsc commented Aug 13, 2018

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.

@bradfitz
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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

@draftcode
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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?

@draftcode
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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.

@bradfitz
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@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.

@draftcode
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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.

@draftcode
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An example that for this: https://play.golang.org/p/OWb6zRUD02r

@rsc
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rsc commented Aug 14, 2018

@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.

@draftcode
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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.

@rsc rsc changed the title proposal: make go-get work for private source code hosting services proposal: cmd/go: define HTTP authentication extension mechanism Aug 20, 2018
@rsc
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rsc commented Aug 20, 2018

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.

@draftcode
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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?
    • If this is a requirement, this means that Go cannot support OS-standard credential management mechanisms.
    • Also this makes it hard to protect credentials. If this is done in stdin/stdout, the credential manager side can do a necessary re-auth.
  • This is just "defining a protocol between Go's toolchain and a user-defined credential manager", right? We do not want to create a password manager like LastPass for this purpose.
  • With a user-defined credential manager, users should be able to:
    • Add an HTTP header (including cookies)
    • Add an SSL client certificate
    • Anything else?

@josharian
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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.

@rsc
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rsc commented Sep 19, 2018

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?

@dmitris
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dmitris commented Sep 25, 2018

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:

  • shell out git ls-remote -q https://git.mycompany.com/org/repo.git first (as now)
  • if it gets a response with an auth prompt: 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 - #24076 (comment)

@draftcode
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Assuming the server returns a meta tag

@dmitris This proposal is for the servers that cannot return meta tags without an auth (see #26232 (comment)). It seems to me that your problem is not related to this.

@rsc rsc modified the milestones: Go1.14, Backlog Oct 9, 2019
@bcmills
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bcmills commented Oct 10, 2019

Just to set expectations: I don't think this will make the 1.14 cycle. (There is too much left to do, and the fixed .netrc support in 1.13 seems to have addressed many of the popular hosting platforms.)

@urandom2
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Would it be possible to break up work so that the community can contribute? I am interested in this issue, but unclear if I could meaningfuly help, short of just landing the feature in isolation.

@bcmills
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bcmills commented Oct 11, 2019

@arnottcr, I don't know of any way to break it up. The bulk of the work, I think, is making sure that everything works properly in conjunction with the GOPROXY fallback sequence and the package-to-module search sequence.

(Essentially, we currently have a two-dimensional search space, and GOAUTH adds a third dimension to search, so we need to figure out exactly what order to traverse those dimensions to avoid breaking things like the GOPROXY privacy properties.)

@nkralles

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@firelizzard18
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Do you have an estimate for when this will be implemented? E.g. 1.15 or 1.16?

@ericsampson
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ericsampson commented Dec 12, 2020

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.

I'm way late to this party, but in case it's of any interest, this is pretty much what Microsoft's NuGet package managers (nuget.exe and dotnet CLI and Visual Studio) do for authenticated package feeds using a shared nuget credential provider

@mjrlee
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mjrlee commented Feb 4, 2021

I'm butting up against this issue in a slightly different way.

We proxy all our traffic to our git server through a kerberos authenticating proxy. Most applications use libcurl at some point, which handles this nicely (performs negotation after receiving a 401).

https://github.com/jcmturner/gokrb5 has a pure go implementation of SPNEGO. I'd be up for writing some GOAUTH handler that generates a preemptive negotiate header.

@shakefu
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shakefu commented Sep 29, 2021

Do you have an estimate for when this will be implemented? E.g. 1.15 or 1.16?

Go 2? ... Would really be nice to see Go and its toolchain have the same first class support for standard auth mechanisms.

@srowles
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srowles commented Dec 13, 2021

Just bumped into this while trying to get at a gitlab instance that was behind a cloudflare auth. So commenting here to add to the use-cases.

I'd like to be able to set, somehow, a custom http header to allow cloudflare access e.g.

cf-access-token: $TOKEN

If I could configure this custom header, in a .netrc style, so that I can just say that matching hosts have to supply the extra header value, it would have solved the access problem early nicely

@pboguslawski
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Client TLS cert auth to private git repos would be nice also: #53197

@Dansyuqri
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Seems like there are a few ways to do authentication, one of them using the header to send a token. I am also facing the same issue as @srowles . As such, would it be useful to split this task into multiple smaller ones? One of them to add the reading of a header and its corresponding value from Go's environment variable (i.e. GOAUTH_HEADER, GOAUTH_HEADER_VALUE)?

@owenhaynes
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owenhaynes commented Jul 25, 2022

Looks like GCP are trying to do stuff with artefact registry now and go module proxy.
https://github.com/GoogleCloudPlatform/artifact-registry-go-tools

So looks like there is a need to support something

AndrewBurian added a commit to AndrewBurian/go that referenced this issue Mar 18, 2023
Creates the GOAUTH env var, and allows for credential helper
invocation to provide arbitrary credentials for module servers.

updates golang#26232
@AndrewBurian
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I am very late to this party it seems, but I might have a bit more to offer than just a +1.

netrc as the only supported authentication mechanism for module proxies doesn't seem to be a passionate issue anywhere, but like @owenhaynes pointed out, module adoption is widespread and having to manage git/ssh credentials for private modules is a growing thorn. I'll go as far as to say I think programatically updating .netrc is probably more a sign of desperate madness than a robust solution.

For better or worse, I didn't find this issue until after I'd taken a stab at fixing it myself. Fortunately, I came to most of the same conclusions this proposal did, with a few exceptions. I agree entirely with avoiding bespoke protocols where good ones exist, but also that existing protocols that leverage plaintext and hardcoded tokens are best left behind.

The few assumptions I think I might have made differently to @bcmills:

  • it is safe to assume prior knowledge of which helpers will be able to provide credentials for what proxies
  • we avoid interactiveness through caching, but if a proxy has a defined credential helper, we don't even try before fetching a cred
  • the myriad of ways that authentication can happen is not a problem space that can be captured in advance, and the protocol for pulling "credentials" needs to be gracefully extensible so future versions of Go can support new mechanisms (e.g. mTLS) without breaking changes to the interaction between go and the helpers

My design is as follows:

The GOAUTH config behaves like GOVCS in that it's an associative config that maps proxy hosts to helpers that can supply them credentials.

The grammar for GOAUTH is GOAUTH=<proxy-glob>!<helper-bin>[;<arg>[; ...]][, ...]. By example:

GOAUTH='*priv.example.com!/usr/local/bin/corp-credhelper;--user=me,proxy.example.com/private/*!my-credtool'

In this, proxy-glob is a host and path that will be matched with module.MatchPrefixPatterns, and an associated helper-bin that is executed with any corresponding arguments. Earlier matches take precedence, and go only invokes one helper per request.

The protocol between go and the helper is borrowed from a system that seems to be working well in the real world: kubernetes and its client.authentication.k8s.io ExecCredential. This is the helper system that kubectl commands use to authenticate to clusters.

GOAUTH plugins must return a HttpCredential object as JSON over stdout. Go will ignore any unknown fields in this object, allowing for future extensibility without breaking changes. As I've defined it, it supports the arbitrary http headers approach, a shorthand for Bearer tokens, and basic auth. I was going to suggest TLS client cert/secret pairs and CA bundle would be a worthy addition as #26232 (comment) mentioned.

The HttpCredential response includes information about how long the provided credentials will be valid for, allowing Go to cache it both in-memory for repeat requests, or on-disk for caching between commands. GOAUTHCACHE points to a file on disk (default to $USER_CONFIG_DIR/.goauthcache) where it's stored. Since I'm not a big fan of writing creds to disk if I don't have to, I am assuming most cred helpers can either choose to handle the caching themselves, or the disk cache can be disabled with GOAUTHCACHE=off.

Test code

I have this implementation "working" in a dev branch: master...AndrewBurian:go:auth-plugins

This is my first time seriously slogging my way through go's test suite, so forgive... everything. It's mostly a PoC so I could see if the design was even a good idea or not, and seems to work as I'd expect.

Git+SSH?

I'm not sure if this helps or hurts the situation with Github and ssh auth #26134.

My understanding after catching up all the discussion here is that go defers everything about the transport of source code outside of module zips to the VSC tool, and so having to configure git separately with auth for modules being served from private VCS feels correct. The focus of GOAUTH is very much for the distribution of private modules, and GOPRIVATE for private VCS.

There may be some weird behaviour if the http authentication allows go to discover the existence of a repo with the initial https go-get=1 request, but then not be able to clone it if git hasn't had credentials configured. I got turned around in the code, but it seems like with the hardcoded VCS handler for Github, go maybe doesn't even bother with the initial get?

I will continue to play around with this, but after finally getting it to all compile my go seamlessly fetches modules with GOPROXY set to only a private Google Cloud Storage bucket and a 3-line script wrapping up gcloud auth print-access-token as a cred helper. In my opinion, it feels like how I would expect private authentication to work coming from git and k8s.

@seankhliao
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maybe instead of implementing the myriad of authentication strategies people may want, we just have a making of module prefixes to plain http proxies
and let the proxies be responsible for the auth

@nkralles
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nkralles commented Mar 22, 2023 via email

@rsj-ioki
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The GOAUTH env var is not yet recognized right? At least on 1.20.4 it is being ignored

@alorle
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alorle commented May 30, 2023

Any news on this?

I've seen that this has been worked on (https://github.com/golang/tools/tree/master/cmd/auth), but as @rsj-ioki says it does not seem that it is fully implemented or available.

@silverwind
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The lack of any authentification mechanism against a GOPROXY is a pretty serious security concern for anyone running their own private proxy because anyone with HTTPS access to the proxy can retrieve all stored modules.

@bcmills bcmills removed their assignment Mar 13, 2024
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