JRE 8 rt.jar is the JAR file for JRE 8 RT (Runtime) libraries. JRE (Java Runtime) 8 is the runtime environment included in JDK 8. JRE 8 rt.jar libraries are divided into 6 packages:

com.* - Internal Oracle and Sun Microsystems libraries
java.* - Standard Java API libraries.
javax.* - Extended Java API libraries.
jdk.* -  JDK supporting libraries.
org.* - Third party libraries.
sun.* - Old libraries developed by Sun Microsystems.

JAR File Information:

Directory of C:\fyicenter\jdk-1.8.0_191\jre\lib
      63,596,151 rt.jar

Here is the list of Java classes of the javax.* package in JRE 1.8.0_191 rt.jar. Java source codes are also provided.

⏎ javax/security/auth/kerberos/package-info.java

/*
 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/**
 * This package contains utility classes related to the Kerberos network
 * authentication protocol. They do not provide much Kerberos support
 * themselves.<p>
 *
 * The Kerberos network authentication protocol is defined in
 * <a href=http://www.ietf.org/rfc/rfc4120.txt>RFC 4120</a>. The Java
 * platform contains support for the client side of Kerberos via the
 * {@link org.ietf.jgss} package. There might also be
 * a login module that implements
 * {@link javax.security.auth.spi.LoginModule LoginModule} to authenticate
 * Kerberos principals.<p>
 *
 * You can provide the name of your default realm and Key Distribution
 * Center (KDC) host for that realm using the system properties
 * {@code java.security.krb5.realm} and {@code java.security.krb5.kdc}.
 * Both properties must be set.
 * Alternatively, the {@code java.security.krb5.conf} system property can
 * be set to the location of an MIT style {@code krb5.conf} configuration
 * file. If none of these system properties are set, the {@code krb5.conf}
 * file is searched for in an implementation-specific manner. Typically,
 * an implementation will first look for a {@code krb5.conf} file in
 * {@code <java-home>/lib/security} and failing that, in an OS-specific
 * location.<p>
 *
 * @since JDK1.4
 */
package javax.security.auth.kerberos;

⏎ javax/security/auth/kerberos/package-info.java

Or download all of them as a single archive file:

File name: jre-rt-javax-1.8.0_191-src.zip
File size: 5381005 bytes
Release date: 2018-10-28
Download 

⇒ JRE 8 rt.jar - org.* Package Source Code

⇐ JRE 8 rt.jar - java.* Package Source Code

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