if there's only one key, return it as the default

Author: Justin Richer

openid-connect-common/src/main/java/org/mitre/jwt/encryption/service/impl/DefaultJwtEncryptionAndDecryptionService.java

@@ -102,7 +102,9 @@ public DefaultJwtEncryptionAndDecryptionService(JWKSetKeyStore keyStore) throws
 throw new IllegalArgumentException("Tried to load a key from a keystore without a 'kid' field: " + key);
 }
 }
+
 buildEncryptersAndDecrypters();
+
 }
 
 
@@ -116,15 +118,29 @@ public void afterPropertiesSet() throws NoSuchAlgorithmException, InvalidKeySpec
 }
 
 public String getDefaultEncryptionKeyId() {
-return defaultEncryptionKeyId;
+if (defaultEncryptionKeyId != null) {
+return defaultEncryptionKeyId;
+} else if (keys.size() == 1) {
+// if there's only one key in the map, it's the default
+return keys.keySet().iterator().next();
+} else {
+return null;
+}
 }
 
 public void setDefaultEncryptionKeyId(String defaultEncryptionKeyId) {
 this.defaultEncryptionKeyId = defaultEncryptionKeyId;
 }
 
 public String getDefaultDecryptionKeyId() {
-return defaultDecryptionKeyId;
+if (defaultDecryptionKeyId != null) {
+return defaultDecryptionKeyId;
+} else if (keys.size() == 1) {
+// if there's only one key in the map, it's the default
+return keys.keySet().iterator().next();
+} else {
+return null;
+}
 }
 
 public void setDefaultDecryptionKeyId(String defaultDecryptionKeyId) {

openid-connect-common/src/main/java/org/mitre/jwt/signer/service/impl/DefaultJwtSigningAndValidationService.java

@@ -109,7 +109,14 @@ public DefaultJwtSigningAndValidationService(JWKSetKeyStore keyStore) throws NoS
  * @return the defaultSignerKeyId
  */
 public String getDefaultSignerKeyId() {
-return defaultSignerKeyId;
+if (defaultSignerKeyId != null) {
+return defaultSignerKeyId;
+} else if (keys.size() == 1) {
+// if there's only one key, it's the default
+return keys.keySet().iterator().next();
+} else {
+return null;
+}
 }
 
 /**