fix: Add missing Javadoc comments to fix checkstyle violations

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: prmoore77

flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/client/oauth/OAuthConfiguration.java

@@ -239,6 +239,13 @@ public Builder tokenUri(@Nullable String tokenUri) throws SQLException {
       return this;
     }
 
+    /**
+     * Sets the OAuth authorization endpoint URL.
+     *
+     * @param authorizationUrl the authorization endpoint URL
+     * @return this builder
+     * @throws SQLException if the URL is invalid
+     */
     public Builder authorizationUrl(@Nullable String authorizationUrl) throws SQLException {
       if (authorizationUrl == null || authorizationUrl.isEmpty()) {
         this.authorizationUri = null;
@@ -252,6 +259,7 @@ public Builder authorizationUrl(@Nullable String authorizationUrl) throws SQLExc
       return this;
     }
 
+    /** Sets the OIDC issuer URL for endpoint auto-discovery. */
     public Builder oidcIssuer(@Nullable String oidcIssuer) {
       this.oidcIssuer = oidcIssuer;
       return this;

flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/client/oauth/PkceGenerator.java

@@ -40,6 +40,11 @@ public PkceGenerator() {
     this(DEFAULT_VERIFIER_LENGTH);
   }
 
+  /**
+   * Creates a new PkceGenerator with a custom verifier length.
+   *
+   * @param verifierLength the length of the code verifier (43-128 characters)
+   */
   public PkceGenerator(int verifierLength) {
     if (verifierLength < 43 || verifierLength > 128) {
       throw new IllegalArgumentException("Verifier length must be between 43 and 128 characters");