Change r.login.microsoftonline.com to login.microsoft.com

README.md

@@ -43,7 +43,7 @@ Acquiring tokens with MSAL Go follows this general three step pattern. There mig
    * Initializing a public client:
 
     ```go
-    publicClientApp, err := public.New("client_id", public.WithAuthority("https://login.microsoftonline.com/Enter_The_Tenant_Name_Here"))
+    publicClientApp, err := public.New("client_id", public.WithAuthority("https://login.microsoft.com/Enter_The_Tenant_Name_Here"))
     ```
 
    * Initializing a confidential client:
@@ -54,7 +54,7 @@ Acquiring tokens with MSAL Go follows this general three step pattern. There mig
     if err != nil {
         return nil, fmt.Errorf("could not create a cred from a secret: %w", err)
     }
-    confidentialClientApp, err := confidential.New("client_id", cred, confidential.WithAuthority("https://login.microsoftonline.com/Enter_The_Tenant_Name_Here"))
+    confidentialClientApp, err := confidential.New("client_id", cred, confidential.WithAuthority("https://login.microsoft.com/Enter_The_Tenant_Name_Here"))
     ```
 
 1. MSAL comes packaged with an in-memory cache. Utilizing the cache is optional, but we would highly recommend it.

apps/internal/oauth/ops/authority/authority.go

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT license.
 
+// TODO(someone): Write a package description and document everything.
 package authority
 
 import (
@@ -28,16 +29,27 @@ const (
 	regionName                        = "REGION_NAME"
 	defaultAPIVersion                 = "2021-10-01"
 	imdsEndpoint                      = "http://169.254.169.254/metadata/instance/compute/location?format=text&api-version=" + defaultAPIVersion
-	defaultHost                       = "login.microsoftonline.com"
-	autoDetectRegion                  = "TryAutoDetect"
+
+	autoDetectRegion = "TryAutoDetect"
+)
+
+// These are various hosts that host AAD Instance discovery endpoints.
+const (
+	defaultHost          = "login.microsoftonline.com"
+	loginMicrosoft       = "login.microsoft.com"
+	loginWindows         = "login.windows.net"
+	loginSTSWindows      = "sts.windows.net"
+	loginMicrosoftOnline = defaultHost
 )
 
+// jsonCaller is an interface that allows us to mock the JSONCall method.
 type jsonCaller interface {
 	JSONCall(ctx context.Context, endpoint string, headers http.Header, qv url.Values, body, resp interface{}) error
 }
 
+// aadTrustedHostList is a list of trusted hosts for AAD.
 var aadTrustedHostList = map[string]bool{
-	"login.windows.net":            true, // Microsoft Azure Worldwide - Used in validation scenarios where host is not this list
+	loginWindows:                   true, // Microsoft Azure Worldwide - Used in validation scenarios where host is not this list
 	"login.chinacloudapi.cn":       true, // Microsoft Azure China
 	"login.microsoftonline.de":     true, // Microsoft Azure Blackforest
 	"login-us.microsoftonline.com": true, // Microsoft Azure US Government - Legacy
@@ -54,6 +66,8 @@ func TrustedHost(host string) bool {
 	return false
 }
 
+// OAuthResponseBase is the base JSON return message for an OAuth call.
+// This is embedded in other calls to get the base fields from every response.
 type OAuthResponseBase struct {
 	Error            string `json:"error"`
 	SubError         string `json:"suberror"`
@@ -442,6 +456,8 @@ func (c Client) GetTenantDiscoveryResponse(ctx context.Context, openIDConfigurat
 	return resp, err
 }
 
+// AADInstanceDiscovery attempts to discover a tenant endpoint (used in OIDC auth with an authorization endpoint).
+// This is done by AAD which allows for aliasing of tenants (windows.sts.net is the same as login.windows.com).
 func (c Client) AADInstanceDiscovery(ctx context.Context, authorityInfo Info) (InstanceDiscoveryResponse, error) {
 	region := ""
 	var err error
@@ -454,8 +470,8 @@ func (c Client) AADInstanceDiscovery(ctx context.Context, authorityInfo Info) (I
 	if region != "" {
 		environment := authorityInfo.Host
 		switch environment {
-		case "login.microsoft.com", "login.windows.net", "sts.windows.net", defaultHost:
-			environment = "r." + defaultHost
+		case loginMicrosoft, loginWindows, loginSTSWindows, defaultHost:
+			environment = loginMicrosoft
 		}
 		resp.TenantDiscoveryEndpoint = fmt.Sprintf(tenantDiscoveryEndpointWithRegion, region, environment, authorityInfo.Tenant)
 		metadata := InstanceDiscoveryMetadata{

apps/internal/oauth/ops/authority/authority_test.go

@@ -267,7 +267,7 @@ func TestAADInstanceDiscoveryWithRegion(t *testing.T) {
 	client := Client{&fakeJSONCaller{}}
 	region := "region"
 	discoveryPath := "tenant/v2.0/.well-known/openid-configuration"
-	publicCloudEndpoint := fmt.Sprintf("https://%s.r.login.microsoftonline.com/%s", region, discoveryPath)
+	publicCloudEndpoint := fmt.Sprintf("https://%s.login.microsoft.com/%s", region, discoveryPath)
 	for _, test := range []struct{ host, expectedEndpoint string }{
 		{"login.chinacloudapi.cn", fmt.Sprintf("https://%s.login.chinacloudapi.cn/%s", region, discoveryPath)},
 		{"login.microsoft.com", publicCloudEndpoint},