Added expectIssuer convenience method.

src/main/java/io/jsonwebtoken/JwtParser.java

@@ -27,6 +27,14 @@ public interface JwtParser {
 
     public static final char SEPARATOR_CHAR = '.';
 
+    /**
+     * Sets an expected value for the issuer claim.
+     *
+     * @param issuer
+     * @return the parser for method chaining.
+     */
+    JwtParser expectIssuer(String issuer);
+
     /**
      * Sets an expected value for the issuedAt claim.
      *

src/main/java/io/jsonwebtoken/impl/DefaultJwtParser.java

@@ -73,6 +73,13 @@ public class DefaultJwtParser implements JwtParser {
         return this;
     }
 
+    @Override
+    public JwtParser expectIssuer(String issuer) {
+        expect(Claims.ISSUER, issuer);
+
+        return this;
+    }
+
     @Override
     public JwtParser expect(String claimName, Object value) {
         if (claimName != null && claimName.length() > 0 && value != null) {
@@ -337,8 +344,12 @@ public class DefaultJwtParser implements JwtParser {
 
     private void validateExpectedClaims(Header header, Claims claims) {
         for (String expectedClaimName : expectedClaims.keySet()) {
-            Object expectedClaimValue = null;
-            Object actualClaimValue = null;
+            Object expectedClaimValue;
+            Object actualClaimValue;
+
+            // since issued at is a date, call the specific method
+            // other methods deal with strings and the more
+            // general method can be used
             if (Claims.ISSUED_AT.equals(expectedClaimName)) {
                 expectedClaimValue = expectedClaims.getIssuedAt();
                 actualClaimValue = claims.getIssuedAt();

src/test/groovy/io/jsonwebtoken/JwtParserTest.groovy

@@ -917,4 +917,68 @@ class JwtParserTest {
             )
         }
     }
+
+    @Test
+    void testParseExpectIssuer_Success() {
+        def issuer = 'A Most Awesome Issuer'
+
+        byte[] key = randomKey()
+
+        String compact = Jwts.builder().signWith(SignatureAlgorithm.HS256, key).
+            setIssuer(issuer).
+            compact()
+
+        Jwt<Header,Claims> jwt = Jwts.parser().setSigningKey(key).
+            expectIssuer(issuer).
+            parseClaimsJws(compact)
+
+        assertEquals jwt.getBody().getIssuer(), issuer
+    }
+
+    @Test
+    void testParseExpectIssuer_Incorrect_Fail() {
+        def goodIssuer = 'A Most Awesome Issuer'
+        def badIssuer = 'A Most Bogus Issuer'
+
+        byte[] key = randomKey()
+
+        String compact = Jwts.builder().signWith(SignatureAlgorithm.HS256, key).
+            setIssuer(badIssuer).
+            compact()
+
+        try {
+            Jwts.parser().setSigningKey(key).
+                expectIssuer(goodIssuer).
+                parseClaimsJws(compact)
+            fail()
+        } catch(IncorrectClaimException e) {
+            assertEquals(
+                String.format(INCORRECT_EXPECTED_CLAIM_MESSAGE_TEMPLATE, Claims.ISSUER, goodIssuer, badIssuer),
+                e.getMessage()
+            )
+        }
+    }
+
+    @Test
+    void testParseExpectIssuer_Missing_Fail() {
+        def issuer = 'A Most Awesome Issuer'
+
+        byte[] key = randomKey()
+
+        String compact = Jwts.builder().signWith(SignatureAlgorithm.HS256, key).
+            setId('id').
+            compact()
+
+        try {
+            Jwts.parser().setSigningKey(key).
+                expectIssuer(issuer).
+                parseClaimsJws(compact)
+            fail()
+        } catch(MissingClaimException e) {
+            assertEquals(
+                String.format(MISSING_EXPECTED_CLAIM_MESSAGE_TEMPLATE, Claims.ISSUER, issuer),
+                e.getMessage()
+            )
+        }
+    }
 }