Allow reuse of host checks for extension authors

Following on the heels of #151, this commit exports the internal logic used to
determine if a host is GHES deployment or a tenant.

Exporting these functions allow extension authors like `github/gh-copilot` to
provide tailored experiences consistently with `gh`.

pkg/auth/auth.go

@@ -62,7 +62,7 @@ func TokenFromEnvOrConfig(host string) (string, string) {
 
 func tokenForHost(cfg *config.Config, host string) (string, string) {
 	host = normalizeHostname(host)
-	if isEnterprise(host) {
+	if IsEnterprise(host) {
 		if token := os.Getenv(ghEnterpriseToken); token != "" {
 			return token, ghEnterpriseToken
 		}
@@ -152,11 +152,11 @@ func defaultHost(cfg *config.Config) (string, string) {
 // TenancyHost is the domain name of a tenancy GitHub instance.
 const tenancyHost = "ghe.com"
 
-func isEnterprise(host string) bool {
-	return host != github && host != localhost && !isTenancy(host)
+func IsEnterprise(host string) bool {
+	return host != github && host != localhost && !IsTenancy(host)
 }
 
-func isTenancy(host string) bool {
+func IsTenancy(host string) bool {
 	return strings.HasSuffix(host, "."+tenancyHost)
 }
 

pkg/auth/auth_test.go

@@ -256,7 +256,43 @@ func TestIsEnterprise(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			out := isEnterprise(tt.host)
+			out := IsEnterprise(tt.host)
+			assert.Equal(t, tt.wantOut, out)
+		})
+	}
+}
+
+func TestIsTenancy(t *testing.T) {
+	tests := []struct {
+		name    string
+		host    string
+		wantOut bool
+	}{
+		{
+			name:    "github",
+			host:    "github.com",
+			wantOut: false,
+		},
+		{
+			name:    "localhost",
+			host:    "github.localhost",
+			wantOut: false,
+		},
+		{
+			name:    "enterprise",
+			host:    "mygithub.com",
+			wantOut: false,
+		},
+		{
+			name:    "tenant",
+			host:    "tenant.ghe.com",
+			wantOut: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			out := IsTenancy(tt.host)
 			assert.Equal(t, tt.wantOut, out)
 		})
 	}