implement API endpoint validator

provider/github-app-token/github-app-token.go

@@ -16,6 +16,7 @@ import (
 
 type githubClient interface {
 	CreateStatus(ctx context.Context, token, owner, repo, ref string, status *github.CreateStatusRequest) (*github.CreateStatusResponse, error)
+	ValidateAPIURL(url string) error
 }
 
 const (
@@ -88,6 +89,9 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 }
 
 func (h *Handler) handle(ctx context.Context, req *requestBody) (*responseBody, error) {
+	if err := h.github.ValidateAPIURL(req.APIURL); err != nil {
+		return nil, err
+	}
 	if err := h.validateGitHubToken(ctx, req); err != nil {
 		return nil, err
 	}

provider/github-app-token/github-app-token_test.go

@@ -10,13 +10,18 @@ import (
 )
 
 type githubClientMock struct {
-	CreateStatusFunc func(ctx context.Context, token, owner, repo, ref string, status *github.CreateStatusRequest) (*github.CreateStatusResponse, error)
+	CreateStatusFunc   func(ctx context.Context, token, owner, repo, ref string, status *github.CreateStatusRequest) (*github.CreateStatusResponse, error)
+	ValidateAPIURLFunc func(url string) error
 }
 
 func (c *githubClientMock) CreateStatus(ctx context.Context, token, owner, repo, ref string, status *github.CreateStatusRequest) (*github.CreateStatusResponse, error) {
 	return c.CreateStatusFunc(ctx, token, owner, repo, ref, status)
 }
 
+func (c *githubClientMock) ValidateAPIURL(url string) error {
+	return c.ValidateAPIURLFunc(url)
+}
+
 func TestValidateGitHubToken(t *testing.T) {
 	h := &Handler{
 		github: &githubClientMock{
@@ -47,6 +52,9 @@ func TestValidateGitHubToken(t *testing.T) {
 					},
 				}, nil
 			},
+			ValidateAPIURLFunc: func(url string) error {
+				return nil
+			},
 		},
 	}
 	err := h.validateGitHubToken(context.Background(), &requestBody{
@@ -96,6 +104,9 @@ func TestValidateGitHubToken_InvalidCreator(t *testing.T) {
 					},
 				}, nil
 			},
+			ValidateAPIURLFunc: func(url string) error {
+				return nil
+			},
 		},
 	}
 	err := h.validateGitHubToken(context.Background(), &requestBody{

provider/github-app-token/github/github.go

@@ -1,6 +1,7 @@
 package github
 
 import (
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -10,7 +11,7 @@ import (
 )
 
 const (
-	githubUserAgent   = "actions-aws-assume-role/1.0"
+	githubUserAgent   = "actions-github-token/1.0"
 	defaultAPIBaseURL = "https://api.github.com"
 )
 
@@ -45,6 +46,24 @@ func NewClient(httpClient *http.Client) *Client {
 	}
 }
 
+func (c *Client) ValidateAPIURL(url string) error {
+	u, err := canonicalURL(url)
+	if err != nil {
+		return err
+	}
+	if u != c.baseURL {
+		if c.baseURL == defaultAPIBaseURL {
+			return errors.New(
+				"it looks that you use GitHub Enterprise Server, " +
+					"but the credential provider doesn't support it. " +
+					"I recommend you to build your own credential provider",
+			)
+		}
+		return errors.New("your api server is not verified by the credential provider")
+	}
+	return nil
+}
+
 type UnexpectedStatusCodeError struct {
 	StatusCode int
 }