| 1 | // Copyright 2019 The Go Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // gitauth uses 'git credential' to implement the GOAUTH protocol described in |
| 6 | // https://golang.org/issue/26232. It expects an absolute path to the working |
| 7 | // directory for the 'git' command as the first command-line argument. |
| 8 | // |
| 9 | // Example GOAUTH usage: |
| 10 | // |
| 11 | // export GOAUTH="gitauth $HOME" |
| 12 | // |
| 13 | // See https://git-scm.com/docs/gitcredentials or run 'man gitcredentials' for |
| 14 | // information on how to configure 'git credential'. |
| 15 | package main |
| 16 | |
| 17 | import ( |
| 18 | "bytes" |
| 19 | "fmt" |
| 20 | exec "golang.org/x/sys/execabs" |
| 21 | "log" |
| 22 | "net/http" |
| 23 | "net/url" |
| 24 | "os" |
| 25 | "path/filepath" |
| 26 | "strings" |
| 27 | ) |
| 28 | |
| 29 | func main() { |
| 30 | if len(os.Args) < 2 || !filepath.IsAbs(os.Args[1]) { |
| 31 | fmt.Fprintf(os.Stderr, "usage: %s WORKDIR [URL]", os.Args[0]) |
| 32 | os.Exit(2) |
| 33 | } |
| 34 | |
| 35 | log.SetPrefix("gitauth: ") |
| 36 | |
| 37 | if len(os.Args) != 3 { |
| 38 | // No explicit URL was passed on the command line, but 'git credential' |
| 39 | // provides no way to enumerate existing credentials. |
| 40 | // Wait for a request for a specific URL. |
| 41 | return |
| 42 | } |
| 43 | |
| 44 | u, err := url.ParseRequestURI(os.Args[2]) |
| 45 | if err != nil { |
| 46 | log.Fatalf("invalid request URI (%v): %q\n", err, os.Args[1]) |
| 47 | } |
| 48 | |
| 49 | var ( |
| 50 | prefix *url.URL |
| 51 | lastHeader http.Header |
| 52 | lastStatus = http.StatusUnauthorized |
| 53 | ) |
| 54 | for lastStatus == http.StatusUnauthorized { |
| 55 | cmd := exec.Command("git", "credential", "fill") |
| 56 | |
| 57 | // We don't want to execute a 'git' command in an arbitrary directory, since |
| 58 | // that opens up a number of config-injection attacks (for example, |
| 59 | // https://golang.org/issue/29230). Instead, we have the user configure a |
| 60 | // directory explicitly on the command line. |
| 61 | cmd.Dir = os.Args[1] |
| 62 | |
| 63 | cmd.Stdin = strings.NewReader(fmt.Sprintf("url=%s\n", u)) |
| 64 | cmd.Stderr = os.Stderr |
| 65 | out, err := cmd.Output() |
| 66 | if err != nil { |
| 67 | log.Fatalf("'git credential fill' failed: %v\n", err) |
| 68 | } |
| 69 | |
| 70 | prefix = new(url.URL) |
| 71 | var username, password string |
| 72 | lines := strings.Split(string(out), "\n") |
| 73 | for _, line := range lines { |
| 74 | frags := strings.SplitN(line, "=", 2) |
| 75 | if len(frags) != 2 { |
| 76 | continue // Ignore unrecognized response lines. |
| 77 | } |
| 78 | switch strings.TrimSpace(frags[0]) { |
| 79 | case "protocol": |
| 80 | prefix.Scheme = frags[1] |
| 81 | case "host": |
| 82 | prefix.Host = frags[1] |
| 83 | case "path": |
| 84 | prefix.Path = frags[1] |
| 85 | case "username": |
| 86 | username = frags[1] |
| 87 | case "password": |
| 88 | password = frags[1] |
| 89 | case "url": |
| 90 | // Write to a local variable instead of updating prefix directly: |
| 91 | // if the url field is malformed, we don't want to invalidate |
| 92 | // information parsed from the protocol, host, and path fields. |
| 93 | u, err := url.ParseRequestURI(frags[1]) |
| 94 | if err == nil { |
| 95 | prefix = u |
| 96 | } else { |
| 97 | log.Printf("malformed URL from 'git credential fill' (%v): %q\n", err, frags[1]) |
| 98 | // Proceed anyway: we might be able to parse the prefix from other fields of the response. |
| 99 | } |
| 100 | } |
| 101 | } |
| 102 | |
| 103 | // Double-check that the URL Git gave us is a prefix of the one we requested. |
| 104 | if !strings.HasPrefix(u.String(), prefix.String()) { |
| 105 | log.Fatalf("requested a credential for %q, but 'git credential fill' provided one for %q\n", u, prefix) |
| 106 | } |
| 107 | |
| 108 | // Send a HEAD request to try to detect whether the credential is valid. |
| 109 | // If the user just typed in a correct password and has caching enabled, |
| 110 | // we don't want to nag them for it again the next time they run a 'go' command. |
| 111 | req, err := http.NewRequest("HEAD", u.String(), nil) |
| 112 | if err != nil { |
| 113 | log.Fatalf("internal error constructing HTTP HEAD request: %v\n", err) |
| 114 | } |
| 115 | req.SetBasicAuth(username, password) |
| 116 | lastHeader = req.Header |
| 117 | resp, err := http.DefaultClient.Do(req) |
| 118 | if err != nil { |
| 119 | log.Printf("HTTPS HEAD request failed to connect: %v\n", err) |
| 120 | // Couldn't verify the credential, but we have no evidence that it is invalid either. |
| 121 | // Proceed, but don't update git's credential cache. |
| 122 | break |
| 123 | } |
| 124 | lastStatus = resp.StatusCode |
| 125 | |
| 126 | if resp.StatusCode != http.StatusOK { |
| 127 | log.Printf("%s: %v %s\n", u, resp.StatusCode, http.StatusText(resp.StatusCode)) |
| 128 | } |
| 129 | |
| 130 | if resp.StatusCode == http.StatusOK || resp.StatusCode == http.StatusUnauthorized { |
| 131 | // We learned something about the credential: it either worked or it was invalid. |
| 132 | // Approve or reject the credential (on a best-effort basis) |
| 133 | // so that the git credential helper can update its cache as appropriate. |
| 134 | action := "approve" |
| 135 | if resp.StatusCode != http.StatusOK { |
| 136 | action = "reject" |
| 137 | } |
| 138 | cmd = exec.Command("git", "credential", action) |
| 139 | cmd.Stderr = os.Stderr |
| 140 | cmd.Stdout = os.Stderr |
| 141 | cmd.Stdin = bytes.NewReader(out) |
| 142 | _ = cmd.Run() |
| 143 | } |
| 144 | } |
| 145 | |
| 146 | // Write out the credential in the format expected by the 'go' command. |
| 147 | fmt.Printf("%s\n\n", prefix) |
| 148 | lastHeader.Write(os.Stdout) |
| 149 | fmt.Println() |
| 150 | } |
| 151 |
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