diff --git a/.circleci/config.yml b/.circleci/config.yml
index 1675c39f..73f58ddb 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -22,14 +22,14 @@ commands:
     steps:
       - run: ./gradlew check jacocoTestReport --continue --console=plain
       - codecov/upload
-  run-api-diff:
-    steps:
-      # run apiDiff task
-      - run: ./gradlew apiDiff
-      - store_artifacts:
-          path: lib/build/reports/apiDiff/apiDiff.txt
-      - store_artifacts:
-          path: lib/build/reports/apiDiff/apiDiff.html
+  # run-api-diff:
+  #   steps:
+  #     # run apiDiff task
+  #     - run: ./gradlew apiDiff
+  #     - store_artifacts:
+  #         path: lib/build/reports/apiDiff/apiDiff.txt
+  #     - store_artifacts:
+  #         path: lib/build/reports/apiDiff/apiDiff.html
 jobs:
   build:
     docker:
@@ -41,21 +41,21 @@ jobs:
       GRADLE_OPTS: '-Dorg.gradle.jvmargs="-Xmx2048m -XX:+HeapDumpOnOutOfMemoryError"'
       _JAVA_OPTIONS: "-Xms512m -Xmx1024m"
       TERM: dumb
-  api-diff:
-    docker:
-      - image: openjdk:11.0-jdk
-    steps:
-      - checkout-and-build
-      - run-api-diff
-    environment:
-      GRADLE_OPTS: '-Dorg.gradle.jvmargs="-Xmx2048m -XX:+HeapDumpOnOutOfMemoryError"'
-      _JAVA_OPTIONS: "-Xms512m -Xmx1024m"
-      TERM: dumb
+  # api-diff:
+  #   docker:
+  #     - image: openjdk:11.0-jdk
+  #   steps:
+  #     - checkout-and-build
+  #     - run-api-diff
+  #   environment:
+  #     GRADLE_OPTS: '-Dorg.gradle.jvmargs="-Xmx2048m -XX:+HeapDumpOnOutOfMemoryError"'
+  #     _JAVA_OPTIONS: "-Xms512m -Xmx1024m"
+  #     TERM: dumb
 
 workflows:
   build-and-test:
     jobs:
       - build
-  api-diff:
-    jobs:
-      - api-diff
+  # api-diff:
+  #   jobs:
+  #     - api-diff
diff --git a/lib/src/main/java/com/auth0/jwt/HeaderParams.java b/lib/src/main/java/com/auth0/jwt/HeaderParams.java
index 7af3c442..1107f313 100644
--- a/lib/src/main/java/com/auth0/jwt/HeaderParams.java
+++ b/lib/src/main/java/com/auth0/jwt/HeaderParams.java
@@ -10,20 +10,20 @@ private HeaderParams() {}
     /**
      * The algorithm used to sign a JWT.
      */
-    public static String ALGORITHM = "alg";
+    public static final String ALGORITHM = "alg";
 
     /**
      * The content type of the JWT.
      */
-    public static String CONTENT_TYPE = "cty";
+    public static final String CONTENT_TYPE = "cty";
 
     /**
      * The media type of the JWT.
      */
-    public static String TYPE = "typ";
+    public static final String TYPE = "typ";
 
     /**
      * The key ID of a JWT used to specify the key for signature validation.
      */
-    public static String KEY_ID = "kid";
+    public static final String KEY_ID = "kid";
 }
diff --git a/lib/src/main/java/com/auth0/jwt/RegisteredClaims.java b/lib/src/main/java/com/auth0/jwt/RegisteredClaims.java
index 8c47eb51..c5509716 100644
--- a/lib/src/main/java/com/auth0/jwt/RegisteredClaims.java
+++ b/lib/src/main/java/com/auth0/jwt/RegisteredClaims.java
@@ -13,43 +13,43 @@ private RegisteredClaims() {
      * The "iss" (issuer) claim identifies the principal that issued the JWT.
      * Refer RFC 7529 <a href="https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.1">Section 4.1.1</a>
      */
-    public static String ISSUER = "iss";
+    public static final String ISSUER = "iss";
 
     /**
      * The "sub" (subject) claim identifies the principal that is the subject of the JWT.
      * Refer RFC 7529 <a href="https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.2">Section 4.1.2</a>
      */
-    public static String SUBJECT = "sub";
+    public static final String SUBJECT = "sub";
 
     /**
      * The "aud" (audience) claim identifies the recipients that the JWT is intended for.
      * Refer RFC 7529 <a href="https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.3">Section 4.1.3</a>
      */
-    public static String AUDIENCE = "aud";
+    public static final String AUDIENCE = "aud";
 
     /**
      * The "exp" (expiration time) claim identifies the expiration time on or after which the JWT MUST NOT be
      * accepted for processing.
      * Refer RFC 7529 <a href="https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.4">Section 4.1.4</a>
      */
-    public static String EXPIRES_AT = "exp";
+    public static final String EXPIRES_AT = "exp";
 
     /**
      * The "nbf" (not before) claim identifies the time before which the JWT MUST NOT be accepted for processing.
      * Refer RFC 7529 <a href="https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.5">Section 4.1.5</a>
      */
-    public static String NOT_BEFORE = "nbf";
+    public static final String NOT_BEFORE = "nbf";
 
     /**
      * The "iat" (issued at) claim identifies the time at which the JWT was issued.
      * Refer RFC 7529 <a href="https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.6">Section 4.1.6</a>
      */
-    public static String ISSUED_AT = "iat";
+    public static final String ISSUED_AT = "iat";
 
     /**
      * The "jti" (JWT ID) claim provides a unique identifier for the JWT.
      * Refer RFC 7529 <a href="https://datatracker.ietf.org/doc/html/rfc7519#section-4.1.7">Section 4.1.7</a>
      */
-    public static String JWT_ID = "jti";
+    public static final String JWT_ID = "jti";
 
 }