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// Copyright 2019 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// gitauth uses 'git credential' to implement the GOAUTH protocol described in
// https://golang.org/issue/26232. It expects an absolute path to the working
// directory for the 'git' command as the first command-line argument.
//
// Example GOAUTH usage:
//
// export GOAUTH="gitauth $HOME"
//
// See https://git-scm.com/docs/gitcredentials or run 'man gitcredentials' for
// information on how to configure 'git credential'.
package main
import (
"bytes"
"fmt"
"log"
"net/http"
"net/url"
"os"
"os/exec"
"path/filepath"
"strings"
)
func main() {
if len(os.Args) < 2 || !filepath.IsAbs(os.Args[1]) {
fmt.Fprintf(os.Stderr, "usage: %s WORKDIR [URL]", os.Args[0])
os.Exit(2)
}
log.SetPrefix("gitauth: ")
if len(os.Args) != 3 {
// No explicit URL was passed on the command line, but 'git credential'
// provides no way to enumerate existing credentials.
// Wait for a request for a specific URL.
return
}
u, err := url.ParseRequestURI(os.Args[2])
if err != nil {
log.Fatalf("invalid request URI (%v): %q\n", err, os.Args[1])
}
var (
prefix *url.URL
lastHeader http.Header
lastStatus = http.StatusUnauthorized
)
for lastStatus == http.StatusUnauthorized {
cmd := exec.Command("git", "credential", "fill")
// We don't want to execute a 'git' command in an arbitrary directory, since
// that opens up a number of config-injection attacks (for example,
// https://golang.org/issue/29230). Instead, we have the user configure a
// directory explicitly on the command line.
cmd.Dir = os.Args[1]
cmd.Stdin = strings.NewReader(fmt.Sprintf("url=%s\n", u))
cmd.Stderr = os.Stderr
out, err := cmd.Output()
if err != nil {
log.Fatalf("'git credential fill' failed: %v\n", err)
}
prefix = new(url.URL)
var username, password string
lines := strings.Split(string(out), "\n")
for _, line := range lines {
frags := strings.SplitN(line, "=", 2)
if len(frags) != 2 {
continue // Ignore unrecognized response lines.
}
switch strings.TrimSpace(frags[0]) {
case "protocol":
prefix.Scheme = frags[1]
case "host":
prefix.Host = frags[1]
case "path":
prefix.Path = frags[1]
case "username":
username = frags[1]
case "password":
password = frags[1]
case "url":
// Write to a local variable instead of updating prefix directly:
// if the url field is malformed, we don't want to invalidate
// information parsed from the protocol, host, and path fields.
u, err := url.ParseRequestURI(frags[1])
if err == nil {
prefix = u
} else {
log.Printf("malformed URL from 'git credential fill' (%v): %q\n", err, frags[1])
// Proceed anyway: we might be able to parse the prefix from other fields of the response.
}
}
}
// Double-check that the URL Git gave us is a prefix of the one we requested.
if !strings.HasPrefix(u.String(), prefix.String()) {
log.Fatalf("requested a credential for %q, but 'git credential fill' provided one for %q\n", u, prefix)
}
// Send a HEAD request to try to detect whether the credential is valid.
// If the user just typed in a correct password and has caching enabled,
// we don't want to nag them for it again the next time they run a 'go' command.
req, err := http.NewRequest("HEAD", u.String(), nil)
if err != nil {
log.Fatalf("internal error constructing HTTP HEAD request: %v\n", err)
}
req.SetBasicAuth(username, password)
lastHeader = req.Header
resp, err := http.DefaultClient.Do(req)
if err != nil {
log.Printf("HTTPS HEAD request failed to connect: %v\n", err)
// Couldn't verify the credential, but we have no evidence that it is invalid either.
// Proceed, but don't update git's credential cache.
break
}
lastStatus = resp.StatusCode
if resp.StatusCode != http.StatusOK {
log.Printf("%s: %v %s\n", u, resp.StatusCode, http.StatusText(resp.StatusCode))
}
if resp.StatusCode == http.StatusOK || resp.StatusCode == http.StatusUnauthorized {
// We learned something about the credential: it either worked or it was invalid.
// Approve or reject the credential (on a best-effort basis)
// so that the git credential helper can update its cache as appropriate.
action := "approve"
if resp.StatusCode != http.StatusOK {
action = "reject"
}
cmd = exec.Command("git", "credential", action)
cmd.Stderr = os.Stderr
cmd.Stdout = os.Stderr
cmd.Stdin = bytes.NewReader(out)
_ = cmd.Run()
}
}
// Write out the credential in the format expected by the 'go' command.
fmt.Printf("%s\n\n", prefix)
lastHeader.Write(os.Stdout)
fmt.Println()
}
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