jira: add JIRA provider

Add JIRA JWT process as described here:
https://developer.atlassian.com/cloud/jira/software/oauth-2-jwt-bearer-token-authorization-grant-type/

* Provides a config struct that matched the `installed` hook response
* Creates a signed JWT as per the JIRA process
* Requests a token with the signed JWT

Fixes #278

Change-Id: Iae6f60578c8a6840ed6603a86f02ff4ac08ba813
Reviewed-on: https://go-review.googlesource.com/102037
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

jira/jira.go

@@ -0,0 +1,167 @@
+// Copyright 2018 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.
+
+// Package jira provides claims and JWT signing for OAuth2 to access JIRA/Confluence.
+package jira
+
+import (
+	"context"
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/base64"
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"golang.org/x/oauth2"
+)
+
+// ClaimSet contains information about the JWT signature according
+// to Atlassian's documentation
+// https://developer.atlassian.com/cloud/jira/software/oauth-2-jwt-bearer-token-authorization-grant-type/
+type ClaimSet struct {
+	Issuer       string `json:"iss"`
+	Subject      string `json:"sub"`
+	InstalledURL string `json:"tnt"` // URL of installed app
+	AuthURL      string `json:"aud"` // URL of auth server
+	ExpiresIn    int64  `json:"exp"` // Must be no later that 60 seconds in the future
+	IssuedAt     int64  `json:"iat"`
+}
+
+var (
+	defaultGrantType = "urn:ietf:params:oauth:grant-type:jwt-bearer"
+	defaultHeader    = map[string]string{
+		"typ": "JWT",
+		"alg": "HS256",
+	}
+)
+
+// Config is the configuration for using JWT to fetch tokens,
+// commonly known as "two-legged OAuth 2.0".
+type Config struct {
+	// BaseURL for your app
+	BaseURL string
+
+	// Subject is the userkey as defined by Atlassian
+	// Different than username (ex: /rest/api/2/user?username=alex)
+	Subject string
+
+	oauth2.Config
+}
+
+// TokenSource returns a JWT TokenSource using the configuration
+// in c and the HTTP client from the provided context.
+func (c *Config) TokenSource(ctx context.Context) oauth2.TokenSource {
+	return oauth2.ReuseTokenSource(nil, jwtSource{ctx, c})
+}
+
+// Client returns an HTTP client wrapping the context's
+// HTTP transport and adding Authorization headers with tokens
+// obtained from c.
+//
+// The returned client and its Transport should not be modified.
+func (c *Config) Client(ctx context.Context) *http.Client {
+	return oauth2.NewClient(ctx, c.TokenSource(ctx))
+}
+
+// jwtSource is a source that always does a signed JWT request for a token.
+// It should typically be wrapped with a reuseTokenSource.
+type jwtSource struct {
+	ctx  context.Context
+	conf *Config
+}
+
+func (js jwtSource) Token() (*oauth2.Token, error) {
+	exp := time.Duration(59) * time.Second
+	claimSet := &ClaimSet{
+		Issuer:       fmt.Sprintf("urn:atlassian:connect:clientid:%s", js.conf.ClientID),
+		Subject:      fmt.Sprintf("urn:atlassian:connect:userkey:%s", js.conf.Subject),
+		InstalledURL: js.conf.BaseURL,
+		AuthURL:      js.conf.Endpoint.AuthURL,
+		IssuedAt:     time.Now().Unix(),
+		ExpiresIn:    time.Now().Add(exp).Unix(),
+	}
+
+	v := url.Values{}
+	v.Set("grant_type", defaultGrantType)
+
+	// Add scopes if they exist;  If not, it defaults to app scopes
+	if scopes := js.conf.Scopes; scopes != nil {
+		upperScopes := make([]string, len(scopes))
+		for _, k := range scopes {
+			upperScopes = append(upperScopes, strings.ToUpper(k))
+		}
+		v.Set("scope", strings.Join(upperScopes, "+"))
+	}
+
+	// Sign claims for assertion
+	assertion, err := sign(js.conf.ClientSecret, claimSet)
+	if err != nil {
+		return nil, err
+	}
+	v.Set("assertion", string(assertion))
+
+	// Fetch access token from auth server
+	hc := oauth2.NewClient(js.ctx, nil)
+	resp, err := hc.PostForm(js.conf.Endpoint.TokenURL, v)
+	if err != nil {
+		return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
+	}
+	defer resp.Body.Close()
+	body, err := ioutil.ReadAll(io.LimitReader(resp.Body, 1<<20))
+	if err != nil {
+		return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
+	}
+	if c := resp.StatusCode; c < 200 || c > 299 {
+		return nil, fmt.Errorf("oauth2: cannot fetch token: %v\nResponse: %s", resp.Status, body)
+	}
+
+	// tokenRes is the JSON response body.
+	var tokenRes struct {
+		AccessToken string `json:"access_token"`
+		TokenType   string `json:"token_type"`
+		ExpiresIn   int64  `json:"expires_in"` // relative seconds from now
+	}
+	if err := json.Unmarshal(body, &tokenRes); err != nil {
+		return nil, fmt.Errorf("oauth2: cannot fetch token: %v", err)
+	}
+	token := &oauth2.Token{
+		AccessToken: tokenRes.AccessToken,
+		TokenType:   tokenRes.TokenType,
+	}
+
+	if secs := tokenRes.ExpiresIn; secs > 0 {
+		token.Expiry = time.Now().Add(time.Duration(secs) * time.Second)
+	}
+	return token, nil
+}
+
+// Sign the claim set with the shared secret
+// Result to be sent as assertion
+func sign(key string, claims *ClaimSet) (string, error) {
+	b, err := json.Marshal(defaultHeader)
+	if err != nil {
+		return "", err
+	}
+	header := base64.RawURLEncoding.EncodeToString(b)
+
+	jsonClaims, err := json.Marshal(claims)
+	if err != nil {
+		return "", err
+	}
+	encodedClaims := strings.TrimRight(base64.URLEncoding.EncodeToString(jsonClaims), "=")
+
+	ss := fmt.Sprintf("%s.%s", header, encodedClaims)
+
+	mac := hmac.New(sha256.New, []byte(key))
+	mac.Write([]byte(ss))
+	signature := mac.Sum(nil)
+
+	return fmt.Sprintf("%s.%s", ss, base64.RawURLEncoding.EncodeToString(signature)), nil
+}

jira/jira_test.go

@@ -0,0 +1,185 @@
+// Copyright 2018 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.
+
+package jira
+
+import (
+	"context"
+	"encoding/base64"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"golang.org/x/oauth2"
+	"golang.org/x/oauth2/jws"
+)
+
+func TestJWTFetch_JSONResponse(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{
+			"access_token": "90d64460d14870c08c81352a05dedd3465940a7c",
+			"token_type": "Bearer",
+			"expires_in": 3600
+		}`))
+	}))
+	defer ts.Close()
+
+	conf := &Config{
+		BaseURL: "https://my.app.com",
+		Subject: "userkey",
+		Config: oauth2.Config{
+			ClientID:     "super_secret_client_id",
+			ClientSecret: "super_shared_secret",
+			Scopes:       []string{"read", "write"},
+			Endpoint: oauth2.Endpoint{
+				AuthURL:  "https://example.com",
+				TokenURL: ts.URL,
+			},
+		},
+	}
+
+	tok, err := conf.TokenSource(context.Background()).Token()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !tok.Valid() {
+		t.Errorf("got invalid token: %v", tok)
+	}
+	if got, want := tok.AccessToken, "90d64460d14870c08c81352a05dedd3465940a7c"; got != want {
+		t.Errorf("access token = %q; want %q", got, want)
+	}
+	if got, want := tok.TokenType, "Bearer"; got != want {
+		t.Errorf("token type = %q; want %q", got, want)
+	}
+	if got := tok.Expiry.IsZero(); got {
+		t.Errorf("token expiry = %v, want none", got)
+	}
+}
+
+func TestJWTFetch_BadResponse(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{"token_type": "Bearer"}`))
+	}))
+	defer ts.Close()
+
+	conf := &Config{
+		BaseURL: "https://my.app.com",
+		Subject: "userkey",
+		Config: oauth2.Config{
+			ClientID:     "super_secret_client_id",
+			ClientSecret: "super_shared_secret",
+			Scopes:       []string{"read", "write"},
+			Endpoint: oauth2.Endpoint{
+				AuthURL:  "https://example.com",
+				TokenURL: ts.URL,
+			},
+		},
+	}
+
+	tok, err := conf.TokenSource(context.Background()).Token()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if tok == nil {
+		t.Fatalf("got nil token; want token")
+	}
+	if tok.Valid() {
+		t.Errorf("got invalid token: %v", tok)
+	}
+	if got, want := tok.AccessToken, ""; got != want {
+		t.Errorf("access token = %q; want %q", got, want)
+	}
+	if got, want := tok.TokenType, "Bearer"; got != want {
+		t.Errorf("token type = %q; want %q", got, want)
+	}
+}
+
+func TestJWTFetch_BadResponseType(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{"access_token":123, "token_type": "Bearer"}`))
+	}))
+	defer ts.Close()
+
+	conf := &Config{
+		BaseURL: "https://my.app.com",
+		Subject: "userkey",
+		Config: oauth2.Config{
+			ClientID:     "super_secret_client_id",
+			ClientSecret: "super_shared_secret",
+			Endpoint: oauth2.Endpoint{
+				AuthURL:  "https://example.com",
+				TokenURL: ts.URL,
+			},
+		},
+	}
+
+	tok, err := conf.TokenSource(context.Background()).Token()
+	if err == nil {
+		t.Error("got a token; expected error")
+		if got, want := tok.AccessToken, ""; got != want {
+			t.Errorf("access token = %q; want %q", got, want)
+		}
+	}
+}
+
+func TestJWTFetch_Assertion(t *testing.T) {
+	var assertion string
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		r.ParseForm()
+		assertion = r.Form.Get("assertion")
+
+		w.Header().Set("Content-Type", "application/json")
+		w.Write([]byte(`{
+			"access_token": "90d64460d14870c08c81352a05dedd3465940a7c",
+			"token_type": "Bearer",
+			"expires_in": 3600
+		}`))
+	}))
+	defer ts.Close()
+
+	conf := &Config{
+		BaseURL: "https://my.app.com",
+		Subject: "userkey",
+		Config: oauth2.Config{
+			ClientID:     "super_secret_client_id",
+			ClientSecret: "super_shared_secret",
+			Endpoint: oauth2.Endpoint{
+				AuthURL:  "https://example.com",
+				TokenURL: ts.URL,
+			},
+		},
+	}
+
+	_, err := conf.TokenSource(context.Background()).Token()
+	if err != nil {
+		t.Fatalf("Failed to fetch token: %v", err)
+	}
+
+	parts := strings.Split(assertion, ".")
+	if len(parts) != 3 {
+		t.Fatalf("assertion = %q; want 3 parts", assertion)
+	}
+	gotjson, err := base64.RawURLEncoding.DecodeString(parts[0])
+	if err != nil {
+		t.Fatalf("invalid token header; err = %v", err)
+	}
+
+	got := jws.Header{}
+	if err := json.Unmarshal(gotjson, &got); err != nil {
+		t.Errorf("failed to unmarshal json token header = %q; err = %v", gotjson, err)
+	}
+
+	want := jws.Header{
+		Algorithm: "HS256",
+		Typ:       "JWT",
+	}
+	if got != want {
+		t.Errorf("access token header = %q; want %q", got, want)
+	}
+}