fix signature hashing for iam (#7100)

* fix signature hashing for iam

* add tests

* address comments

* Update weed/s3api/auto_signature_v4_test.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* indention

* fix test

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

weed/s3api/auto_signature_v4_test.go

@@ -1198,6 +1198,109 @@ func TestGitHubIssue7080Scenario(t *testing.T) {
 	assert.Equal(t, testPayload, string(bodyBytes))
 }
 
+// TestIAMSignatureServiceMatching tests that IAM requests use the correct service in signature computation
+// This reproduces the bug described in GitHub issue #7080 where the service was hardcoded to "s3"
+func TestIAMSignatureServiceMatching(t *testing.T) {
+	// Create test IAM instance
+	iam := &IdentityAccessManagement{}
+
+	// Load test configuration with credentials that match the logs
+	err := iam.loadS3ApiConfiguration(&iam_pb.S3ApiConfiguration{
+		Identities: []*iam_pb.Identity{
+			{
+				Name: "power_user",
+				Credentials: []*iam_pb.Credential{
+					{
+						AccessKey: "power_user_key",
+						SecretKey: "power_user_secret",
+					},
+				},
+				Actions: []string{"Admin"},
+			},
+		},
+	})
+	assert.NoError(t, err)
+
+	// Use the exact payload and headers from the failing logs
+	testPayload := "Action=CreateAccessKey&UserName=admin&Version=2010-05-08"
+
+	// Create request exactly as shown in logs
+	req, err := http.NewRequest("POST", "http://localhost:8111/", strings.NewReader(testPayload))
+	assert.NoError(t, err)
+
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded; charset=utf-8")
+	req.Header.Set("Host", "localhost:8111")
+	req.Header.Set("X-Amz-Date", "20250805T082934Z")
+
+	// Calculate the expected signature using the correct IAM service
+	// This simulates what botocore/AWS SDK would calculate
+	credentialScope := "20250805/us-east-1/iam/aws4_request"
+
+	// Calculate the actual payload hash for our test payload
+	actualPayloadHash := getSHA256Hash([]byte(testPayload))
+
+	// Build the canonical request with the actual payload hash
+	canonicalRequest := "POST\n/\n\ncontent-type:application/x-www-form-urlencoded; charset=utf-8\nhost:localhost:8111\nx-amz-date:20250805T082934Z\n\ncontent-type;host;x-amz-date\n" + actualPayloadHash
+
+	// Calculate the canonical request hash
+	canonicalRequestHash := getSHA256Hash([]byte(canonicalRequest))
+
+	// Build the string to sign
+	stringToSign := "AWS4-HMAC-SHA256\n20250805T082934Z\n" + credentialScope + "\n" + canonicalRequestHash
+
+	// Calculate expected signature using IAM service (what client sends)
+	expectedSigningKey := getSigningKey("power_user_secret", "20250805", "us-east-1", "iam")
+	expectedSignature := getSignature(expectedSigningKey, stringToSign)
+
+	// Create authorization header with the correct signature
+	authHeader := "AWS4-HMAC-SHA256 Credential=power_user_key/" + credentialScope +
+		", SignedHeaders=content-type;host;x-amz-date, Signature=" + expectedSignature
+	req.Header.Set("Authorization", authHeader)
+
+	// Now test that SeaweedFS computes the same signature with our fix
+	identity, errCode := iam.doesSignatureMatch(actualPayloadHash, req)
+
+	// With the fix, the signatures should match and we should get a successful authentication
+	assert.Equal(t, s3err.ErrNone, errCode)
+	assert.NotNil(t, identity)
+	assert.Equal(t, "power_user", identity.Name)
+}
+
+// TestStreamingSignatureServiceField tests that the s3ChunkedReader struct correctly stores the service
+// This verifies the fix for streaming uploads where getChunkSignature was hardcoding "s3"
+func TestStreamingSignatureServiceField(t *testing.T) {
+	// Test that the s3ChunkedReader correctly uses the service field
+	// Create a mock s3ChunkedReader with IAM service
+	chunkedReader := &s3ChunkedReader{
+		seedDate:      time.Now(),
+		region:        "us-east-1",
+		service:       "iam", // This should be used instead of hardcoded "s3"
+		seedSignature: "testsignature",
+		cred: &Credential{
+			AccessKey: "testkey",
+			SecretKey: "testsecret",
+		},
+	}
+
+	// Test that getScope is called with the correct service
+	scope := getScope(chunkedReader.seedDate, chunkedReader.region, chunkedReader.service)
+	assert.Contains(t, scope, "/iam/aws4_request")
+	assert.NotContains(t, scope, "/s3/aws4_request")
+
+	// Test that getSigningKey would be called with the correct service
+	signingKey := getSigningKey(
+		chunkedReader.cred.SecretKey,
+		chunkedReader.seedDate.Format(yyyymmdd),
+		chunkedReader.region,
+		chunkedReader.service,
+	)
+	assert.NotNil(t, signingKey)
+
+	// The main point is that chunkedReader.service is "iam" and gets used correctly
+	// This ensures that IAM streaming uploads will use "iam" service instead of hardcoded "s3"
+	assert.Equal(t, "iam", chunkedReader.service)
+}
+
 // Test that large IAM request bodies are truncated for security (DoS prevention)
 func TestIAMLargeBodySecurityLimit(t *testing.T) {
 	// Create test IAM instance