Repository: microsoft/go-mssqldb
Pull request #227 (2024-11-25 18:38:41)

Fix error checks during certificatePath reading and parsing in azuread
Before this PR certificate-based authentication (in case of a `ActiveDirectoryServicePrincipal` or `ActiveDirectoryApplication` fed auth) would panic (nil pointer dereference at `github.com/microsoft/go-mssqldb@v1.7.2/azuread/configuration.go:228`) because of wrong error checks.

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All modified and coverable lines are covered by tests :white_check_mark:
> Project coverage is 74.40%. Comparing base [(`573423d`)](https://app.codecov.io/gh/microsoft/go-mssqldb/commit/573423d6141d93d52df6cde94181aef76719e857?dropdown=coverage&el=desc&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft) to head [(`0850e76`)](https://app.codecov.io/gh/microsoft/go-mssqldb/commit/0850e76aff122d4d4d596e0b6db8a2248998eee1?dropdown=coverage&el=desc&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=microsoft).

<details><summary>Additional details and impacted files</summary>


```diff
@@            Coverage Diff             @@
##             main     #227      +/-   ##
==========================================
- Coverage   74.87%   74.40%   -0.48%     
==========================================
  Files          32       31       -1     
  Lines        6397     6388       -9     
==========================================
- Hits         4790     4753      -37     
- Misses       1325     1352      +27     
- Partials      282      283       +1     
```

</details>

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shueybubbles: thx for the PR.

Yikes, this is a bad test hole. Can you pls add a test to at least verify the negative case of a missing cert?
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Patch:
diff --git a/azuread/configuration.go b/azuread/configuration.go
index 8c274a1..7876ae0 100644
--- a/azuread/configuration.go
+++ b/azuread/configuration.go
@@ -184,11 +184,11 @@ func (p *azureFedAuthConfig) provideActiveDirectoryToken(ctx context.Context, se
 		case p.certificatePath != "":
 			var certData []byte
 			certData, err = os.ReadFile(p.certificatePath)
-			if err != nil {
+			if err == nil {
 				var certs []*x509.Certificate
 				var key crypto.PrivateKey
 				certs, key, err = azidentity.ParseCertificates(certData, []byte(p.clientSecret))
-				if err != nil {
+				if err == nil {
 					cred, err = azidentity.NewClientCertificateCredential(tenant, p.clientID, certs, key, nil)
 				}
 			}


Test patch:
diff --git a/azuread/configuration_test.go b/azuread/configuration_test.go
index 0662df7..013a97a 100644
--- a/azuread/configuration_test.go
+++ b/azuread/configuration_test.go
@@ -4,7 +4,13 @@
 package azuread
 
 import (
+	"context"
+	"errors"
+	"io/fs"
+	"net/url"
+	"os"
 	"reflect"
+	"strings"
 	"testing"
 
 	mssql "github.com/microsoft/go-mssqldb"
@@ -137,3 +143,73 @@ func TestValidateParameters(t *testing.T) {
 		}
 	}
 }
+
+func TestProvideActiveDirectoryTokenValidations(t *testing.T) {
+	nonExistentCertPath := os.TempDir() + "non_existent_cert.pem"
+
+	f, err := os.CreateTemp("", "malformed_cert.pem")
+	if err != nil {
+		t.Fatalf("create temporary file: %v", err)
+	}
+	if err = f.Truncate(0); err != nil {
+		t.Fatalf("truncate temporary file: %v", err)
+	}
+	if _, err = f.Write([]byte("malformed")); err != nil {
+		t.Fatalf("write to temporary file: %v", err)
+	}
+	if err = f.Close(); err != nil {
+		t.Fatalf("close temporary file: %v", err)
+	}
+	malformedCertPath := f.Name()
+	t.Cleanup(func() { _ = os.Remove(malformedCertPath) })
+
+	tests := []struct {
+		name                string
+		dsn                 string
+		expectedErr         error
+		expectedErrContains string
+	}{
+		{
+			name: "ActiveDirectoryServicePrincipal_cert_not_found",
+			dsn: `sqlserver://someserver.database.windows.net?` +
+				`user id=` + url.QueryEscape("my-app-id@my-tenant-id") + "&" +
+				`fedauth=ActiveDirectoryServicePrincipal` + "&" +
+				`clientcertpath=` + nonExistentCertPath + "&" +
+				`applicationclientid=someguid`,
+			expectedErr: fs.ErrNotExist,
+		},
+		{
+			name: "ActiveDirectoryServicePrincipal_cert_malformed",
+			dsn: `sqlserver://someserver.database.windows.net?` +
+				`user id=` + url.QueryEscape("my-app-id@my-tenant-id") + "&" +
+				`fedauth=ActiveDirectoryServicePrincipal` + "&" +
+				`clientcertpath=` + malformedCertPath + "&" +
+				`applicationclientid=someguid`,
+			expectedErrContains: "error reading P12 data",
+		},
+	}
+	for _, tst := range tests {
+		t.Run(tst.name, func(t *testing.T) {
+			config, err := parse(tst.dsn)
+			if err != nil {
+				t.Errorf("Unexpected parse error: %v", err)
+				return
+			}
+			_, err = config.provideActiveDirectoryToken(context.Background(), "", "authority/tenant")
+			if err == nil {
+				t.Errorf("Expected error but got nil")
+				return
+			}
+			if tst.expectedErr != nil {
+				if !errors.Is(err, tst.expectedErr) {
+					t.Errorf("Expected error '%v' but got err = %v", tst.expectedErr, err)
+				}
+			}
+			if tst.expectedErrContains != "" {
+				if !strings.Contains(err.Error(), tst.expectedErrContains) {
+					return
+				}
+			}
+		})
+	}
+}