feat: Add support for audience in authorization request

Author: abhisek

Diff for: device/device_flow.go

@@ -54,12 +54,29 @@ type CodeResponse struct {
 	Interval int
 }
 
+// Function signature for setting additional form values.
+type AuthRequestFn func(*url.Values)
+
+func WithAudience(audience string) AuthRequestFn {
+	return func(values *url.Values) {
+		if audience != "" {
+			values.Add("audience", audience)
+		}
+	}
+}
+
 // RequestCode initiates the authorization flow by requesting a code from uri.
-func RequestCode(c httpClient, uri string, clientID string, scopes []string) (*CodeResponse, error) {
-	resp, err := api.PostForm(c, uri, url.Values{
+func RequestCode(c httpClient, uri string, clientID string, scopes []string, extra ...AuthRequestFn) (*CodeResponse, error) {
+	values := url.Values{
 		"client_id": {clientID},
 		"scope":     {strings.Join(scopes, " ")},
-	})
+	}
+
+	for _, fn := range extra {
+		fn(&values)
+	}
+
+	resp, err := api.PostForm(c, uri, values)
 	if err != nil {
 		return nil, err
 	}

Diff for: device/device_flow_test.go

@@ -51,6 +51,7 @@ func TestRequestCode(t *testing.T) {
 		url      string
 		clientID string
 		scopes   []string
+		audience string
 	}
 	tests := []struct {
 		name    string
@@ -126,6 +127,42 @@ func TestRequestCode(t *testing.T) {
 				},
 			},
 		},
+		{
+			name: "with audience",
+			args: args{
+				http: apiClient{
+					stubs: []apiStub{
+						{
+							body:        "verification_uri=http://verify.me&interval=5&expires_in=99&device_code=DEVIC&user_code=123-abc&verification_uri_complete=http://verify.me/?code=123-abc",
+							status:      200,
+							contentType: "application/x-www-form-urlencoded; charset=utf-8",
+						},
+					},
+				},
+				url:      "https://github.com/oauth",
+				clientID: "CLIENT-ID",
+				scopes:   []string{"repo", "gist"},
+				audience: "https://api.github.com",
+			},
+			want: &CodeResponse{
+				DeviceCode:              "DEVIC",
+				UserCode:                "123-abc",
+				VerificationURI:         "http://verify.me",
+				VerificationURIComplete: "http://verify.me/?code=123-abc",
+				ExpiresIn:               99,
+				Interval:                5,
+			},
+			posts: []postArgs{
+				{
+					url: "https://github.com/oauth",
+					params: url.Values{
+						"client_id": {"CLIENT-ID"},
+						"scope":     {"repo gist"},
+						"audience":  {"https://api.github.com"},
+					},
+				},
+			},
+		},
 		{
 			name: "unsupported",
 			args: args{
@@ -237,7 +274,8 @@ func TestRequestCode(t *testing.T) {
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			got, err := RequestCode(&tt.args.http, tt.args.url, tt.args.clientID, tt.args.scopes)
+			got, err := RequestCode(&tt.args.http, tt.args.url,
+				tt.args.clientID, tt.args.scopes, WithAudience(tt.args.audience))
 			if (err != nil) != (tt.wantErr != "") {
 				t.Errorf("RequestCode() error = %v, wantErr %v", err, tt.wantErr)
 				return

Diff for: oauth.go

@@ -45,6 +45,8 @@ type Flow struct {
 	Host *Host
 	// OAuth scopes to request from the user.
 	Scopes []string
+	// OAuth audience to request from the user.
+	Audience string
 	// OAuth application ID.
 	ClientID string
 	// OAuth application secret. Only applicable in web application flow.

Diff for: oauth_device.go

@@ -34,7 +34,8 @@ func (oa *Flow) DeviceFlow() (*api.AccessToken, error) {
 		host = GitHubHost("https://" + oa.Hostname)
 	}
 
-	code, err := device.RequestCode(httpClient, host.DeviceCodeURL, oa.ClientID, oa.Scopes)
+	code, err := device.RequestCode(httpClient, host.DeviceCodeURL,
+		oa.ClientID, oa.Scopes, device.WithAudience(oa.Audience))
 	if err != nil {
 		return nil, err
 	}

Diff for: oauth_webapp.go

@@ -27,6 +27,7 @@ func (oa *Flow) WebAppFlow() (*api.AccessToken, error) {
 		ClientID:    oa.ClientID,
 		RedirectURI: oa.CallbackURI,
 		Scopes:      oa.Scopes,
+		Audience:    oa.Audience,
 		AllowSignup: true,
 	}
 	browserURL, err := flow.BrowserURL(host.AuthorizeURL, params)

Diff for: webapp/webapp_flow.go

@@ -47,6 +47,7 @@ type BrowserParams struct {
 	ClientID    string
 	RedirectURI string
 	Scopes      []string
+	Audience    string
 	LoginHandle string
 	AllowSignup bool
 }
@@ -68,6 +69,10 @@ func (flow *Flow) BrowserURL(baseURL string, params BrowserParams) (string, erro
 	q.Set("redirect_uri", ru.String())
 	q.Set("scope", strings.Join(params.Scopes, " "))
 	q.Set("state", flow.state)
+
+	if params.Audience != "" {
+		q.Set("audience", params.Audience)
+	}
 	if params.LoginHandle != "" {
 		q.Set("login", params.LoginHandle)
 	}

Diff for: webapp/webapp_flow_test.go

@@ -51,6 +51,24 @@ func TestFlow_BrowserURL(t *testing.T) {
 			want:    "https://github.com/authorize?client_id=CLIENT-ID&redirect_uri=http%3A%2F%2F127.0.0.1%3A12345%2Fhello&scope=repo+read%3Aorg&state=xy%2Fz",
 			wantErr: false,
 		},
+		{
+			name: "happy path with audience",
+			fields: fields{
+				server: server,
+				state:  "xy/z",
+			},
+			args: args{
+				baseURL: "https://github.com/authorize",
+				params: BrowserParams{
+					ClientID:    "CLIENT-ID",
+					RedirectURI: "http://127.0.0.1/hello",
+					Scopes:      []string{"repo", "read:org"},
+					AllowSignup: true,
+					Audience:    "https://api.github.com",
+				},
+			},
+			want: "https://github.com/authorize?audience=https%3A%2F%2Fapi.github.com&client_id=CLIENT-ID&redirect_uri=http%3A%2F%2F127.0.0.1%3A12345%2Fhello&scope=repo+read%3Aorg&state=xy%2Fz",
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {