https://tomcat.apache.org/: Tomcat Servlet Engine Core Classes and Standard implementations 
/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.catalina.authenticator;

import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.security.Principal;

import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import org.apache.catalina.connector.Request;
import org.apache.juli.logging.Log;
import org.apache.juli.logging.LogFactory;
import org.apache.tomcat.util.buf.ByteChunk;
import org.apache.tomcat.util.buf.MessageBytes;
import org.apache.tomcat.util.codec.binary.Base64;


An Authenticator and Valve implementation of HTTP BASIC
Authentication, as outlined in RFC 2617:  "HTTP Authentication: Basic
and Digest Access Authentication."

Author:Craig R. McClanahan
/**
 * An <b>Authenticator</b> and <b>Valve</b> implementation of HTTP BASIC
 * Authentication, as outlined in RFC 2617:  "HTTP Authentication: Basic
 * and Digest Access Authentication."
 *
 * @author Craig R. McClanahan
 */
public class BasicAuthenticator extends AuthenticatorBase {

    private final Log log = LogFactory.getLog(BasicAuthenticator.class); // must not be static

    private Charset charset = StandardCharsets.ISO_8859_1;
    private String charsetString = null;
    private boolean trimCredentials = true;


    public String getCharset() {
        return charsetString;
    }


    public void setCharset(String charsetString) {
        // Only acceptable options are null, "" or "UTF-8" (case insensitive)
        if (charsetString == null || charsetString.isEmpty()) {
            charset = StandardCharsets.ISO_8859_1;
        } else if ("UTF-8".equalsIgnoreCase(charsetString)) {
            charset = StandardCharsets.UTF_8;
        } else {
            throw new IllegalArgumentException(sm.getString("basicAuthenticator.invalidCharset"));
        }
        this.charsetString = charsetString;
    }



    public boolean getTrimCredentials() {
        return trimCredentials;
    }


    public void setTrimCredentials(boolean trimCredentials) {
        this.trimCredentials = trimCredentials;
    }


    @Override
    protected boolean doAuthenticate(Request request, HttpServletResponse response)
            throws IOException {

        if (checkForCachedAuthentication(request, response, true)) {
            return true;
        }

        // Validate any credentials already included with this request
        MessageBytes authorization =
            request.getCoyoteRequest().getMimeHeaders()
            .getValue("authorization");

        if (authorization != null) {
            authorization.toBytes();
            ByteChunk authorizationBC = authorization.getByteChunk();
            BasicCredentials credentials = null;
            try {
                credentials = new BasicCredentials(authorizationBC, charset, getTrimCredentials());
                String username = credentials.getUsername();
                String password = credentials.getPassword();

                Principal principal = context.getRealm().authenticate(username, password);
                if (principal != null) {
                    register(request, response, principal,
                        HttpServletRequest.BASIC_AUTH, username, password);
                    return true;
                }
            }
            catch (IllegalArgumentException iae) {
                if (log.isDebugEnabled()) {
                    log.debug("Invalid Authorization" + iae.getMessage());
                }
            }
        }

        // the request could not be authenticated, so reissue the challenge
        StringBuilder value = new StringBuilder(16);
        value.append("Basic realm=\"");
        value.append(getRealmName(context));
        value.append('\"');
        if (charsetString != null && !charsetString.isEmpty()) {
            value.append(", charset=");
            value.append(charsetString);
        }
        response.setHeader(AUTH_HEADER_NAME, value.toString());
        response.sendError(HttpServletResponse.SC_UNAUTHORIZED);
        return false;

    }

    @Override
    protected String getAuthMethod() {
        return HttpServletRequest.BASIC_AUTH;
    }


    
Parser for an HTTP Authorization header for BASIC authentication
as per RFC 2617 section 2, and the Base64 encoded credentials as
per RFC 2045 section 6.8.

/**
     * Parser for an HTTP Authorization header for BASIC authentication
     * as per RFC 2617 section 2, and the Base64 encoded credentials as
     * per RFC 2045 section 6.8.
     */
    public static class BasicCredentials {

        // the only authentication method supported by this parser
        // note: we include single white space as its delimiter
        private static final String METHOD = "basic ";

        private final Charset charset;
        private final boolean trimCredentials;
        private final ByteChunk authorization;
        private final int initialOffset;
        private int base64blobOffset;
        private int base64blobLength;

        private String username = null;
        private String password = null;

        
Parse the HTTP Authorization header for BASIC authentication
as per RFC 2617 section 2, and the Base64 encoded credentials
as per RFC 2045 section 6.8.

Params:
  • input –           The header value to parse in-place
  • charset –         The character set to use to convert the bytes
                       to a string
  • trimCredentials – Should leading and trailing whitespace be
                       removed from the parsed credentials
Throws:
/**
         * Parse the HTTP Authorization header for BASIC authentication
         * as per RFC 2617 section 2, and the Base64 encoded credentials
         * as per RFC 2045 section 6.8.
         *
         * @param input           The header value to parse in-place
         * @param charset         The character set to use to convert the bytes
         *                        to a string
         * @param trimCredentials Should leading and trailing whitespace be
         *                        removed from the parsed credentials
         *
         * @throws IllegalArgumentException If the header does not conform
         *                                  to RFC 2617
         */
        public BasicCredentials(ByteChunk input, Charset charset, boolean trimCredentials)
                throws IllegalArgumentException {
            authorization = input;
            initialOffset = input.getOffset();
            this.charset = charset;
            this.trimCredentials = trimCredentials;

            parseMethod();
            byte[] decoded = parseBase64();
            parseCredentials(decoded);
        }

        
Trivial accessor.

Returns: the decoded username token as a String, which is
         never be null, but can be empty.
/**
         * Trivial accessor.
         *
         * @return  the decoded username token as a String, which is
         *          never be <code>null</code>, but can be empty.
         */
        public String getUsername() {
            return username;
        }

        
Trivial accessor.

Returns: the decoded password token as a String, or null
         if no password was found in the credentials.
/**
         * Trivial accessor.
         *
         * @return  the decoded password token as a String, or <code>null</code>
         *          if no password was found in the credentials.
         */
        public String getPassword() {
            return password;
        }

        /*
         * The authorization method string is case-insensitive and must
         * hae at least one space character as a delimiter.
         */
        private void parseMethod() throws IllegalArgumentException {
            if (authorization.startsWithIgnoreCase(METHOD, 0)) {
                // step past the auth method name
                base64blobOffset = initialOffset + METHOD.length();
                base64blobLength = authorization.getLength() - METHOD.length();
            } else {
                // is this possible, or permitted?
                throw new IllegalArgumentException(
                        "Authorization header method is not \"Basic\"");
            }
        }
        /*
         * Decode the base64-user-pass token, which RFC 2617 states
         * can be longer than the 76 characters per line limit defined
         * in RFC 2045. The base64 decoder will ignore embedded line
         * break characters as well as surplus surrounding white space.
         */
        private byte[] parseBase64() throws IllegalArgumentException {
            byte[] decoded = Base64.decodeBase64(
                        authorization.getBuffer(),
                        base64blobOffset, base64blobLength);
            //  restore original offset
            authorization.setOffset(initialOffset);
            if (decoded == null) {
                throw new IllegalArgumentException(
                        "Basic Authorization credentials are not Base64");
            }
            return decoded;
        }

        /*
         * Extract the mandatory username token and separate it from the
         * optional password token. Tolerate surplus surrounding white space.
         */
        private void parseCredentials(byte[] decoded)
                throws IllegalArgumentException {

            int colon = -1;
            for (int i = 0; i < decoded.length; i++) {
                if (decoded[i] == ':') {
                    colon = i;
                    break;
                }
            }

            if (colon < 0) {
                username = new String(decoded, charset);
                // password will remain null!
            } else {
                username = new String(decoded, 0, colon, charset);
                password = new String(decoded, colon + 1, decoded.length - colon - 1, charset);
                // tolerate surplus white space around credentials
                if (password.length() > 1 && trimCredentials) {
                    password = password.trim();
                }
            }
            // tolerate surplus white space around credentials
            if (username.length() > 1 && trimCredentials) {
                username = username.trim();
            }
        }
    }
}