Fix extraction of the response issuer

A ">1" in place of a ">0" was causing the inability to extract the
Response issuer(s) correctly.
Added a test case to check this.
Fixed another test case that should (IMHO) return an error regarding
the issuer, rather than the signature.

Author: mauromol

core/src/main/java/com/onelogin/saml2/authn/SamlResponse.java

@@ -717,7 +717,7 @@ public List<String> getIssuers() throws XPathExpressionException, ValidationErro
 		List<String> issuers = new ArrayList<String>();
 		String value;
 		NodeList responseIssuer = Util.query(samlResponseDocument, "/samlp:Response/saml:Issuer");
-		if (responseIssuer.getLength() > 1) {
+		if (responseIssuer.getLength() > 0) {
 			if (responseIssuer.getLength() == 1) {
 				value = responseIssuer.item(0).getTextContent();
 				if (!issuers.contains(value)) {

core/src/test/java/com/onelogin/saml2/test/authn/AuthnResponseTest.java

@@ -875,6 +875,32 @@ public void testGetIssuers() throws IOException, Error, XPathExpressionException
 		assertEquals(expectedIssuers, samlResponse.getIssuers());
 	}
 
+	/**
+	 * Tests the getIssuers method of SamlResponse
+	 * <p>
+	 * Case: different issuers for response and assertion
+	 *
+	 * @throws Error
+	 * @throws IOException
+	 * @throws ValidationError
+	 * @throws SettingsException
+	 * @throws SAXException
+	 * @throws ParserConfigurationException
+	 * @throws XPathExpressionException
+	 *
+	 * @see com.onelogin.saml2.authn.SamlResponse#getIssuers
+	 */
+	@Test
+	public void testGetIssuersDifferentIssuers() throws IOException, Error, XPathExpressionException, ParserConfigurationException, SAXException, SettingsException, ValidationError {
+		Saml2Settings settings = new SettingsBuilder().fromFile("config/config.my.properties").build();
+		String samlResponseEncoded = Util.getFileAsString("data/responses/invalids/different_issuers.xml.base64");
+		SamlResponse samlResponse = new SamlResponse(settings, newHttpRequest(samlResponseEncoded));
+		List<String> expectedIssuers = new ArrayList<String>();
+		expectedIssuers.add("https://response-issuer.com");
+		expectedIssuers.add("https://assertion-issuer.com");
+		assertEquals(expectedIssuers, samlResponse.getIssuers());
+	}
+
 	/**
 	 * Tests the getIssuers method of SamlResponse
 	 * Case: Issuer of the assertion not found
@@ -1787,8 +1813,7 @@ public void testIsInValidIssuer() throws IOException, Error, XPathExpressionExce
 		settings.setStrict(true);
 		samlResponse = new SamlResponse(settings, newHttpRequest(samlResponseEncoded));
 		assertFalse(samlResponse.isValid());
-		assertEquals("No Signature found. SAML Response rejected", samlResponse.getError());
-		
+		assertEquals("Invalid issuer in the Assertion/Response. Was 'http://invalid.isser.example.com/', but expected 'http://idp.example.com/'", samlResponse.getError());
 	}
 
 	/**

core/src/test/resources/data/responses/invalids/different_issuers.xml.base64

@@ -0,0 +1 @@
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