Add Basic Authentication Consumer

Issue: SPR-16913

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -20,6 +20,8 @@ import java.io.Serializable;
 import java.net.InetSocketAddress;
 import java.net.URI;
 import java.nio.charset.Charset;
+import java.nio.charset.CharsetEncoder;
+import java.nio.charset.StandardCharsets;
 import java.text.DecimalFormat;
 import java.text.DecimalFormatSymbols;
 import java.time.Instant;
@@ -28,6 +30,7 @@ import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
 import java.time.format.DateTimeParseException;
 import java.util.ArrayList;
+import java.util.Base64;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.EnumSet;
@@ -38,6 +41,8 @@ import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
+import java.util.function.Consumer;
+import java.util.function.Supplier;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -1564,4 +1569,88 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 		return (headers.readOnly ? headers : new HttpHeaders(headers, true));
 	}
 
+	/**
+	 * Returns a {@code HttpHeaders} consumer that adds Basic Authentication.
+	 * More specifically: a consumer that adds an {@linkplain #AUTHORIZATION
+	 * Authorization} header based on the given username and password. Meant
+	 * to be used in combination with
+	 * {@link org.springframework.web.reactive.function.client.WebClient.RequestHeadersSpec#headers(java.util.function.Consumer)}.
+	 * <p>Note that Basic Authentication only supports characters in the
+	 * {@linkplain StandardCharsets#ISO_8859_1 ISO-8859-1} character set.
+	 *
+	 * @param username the username
+	 * @param password the password
+	 * @return a consumer that adds a Basic Authentication header
+	 */
+	public static Consumer<HttpHeaders> basicAuthenticationConsumer(String username,String password) {
+		return basicAuthenticationConsumer(() -> username, () -> password);
+
+	}
+
+	/**
+	 * Returns a {@code HttpHeaders} consumer that adds Basic Authentication.
+	 * More specifically: a consumer that adds an {@linkplain #AUTHORIZATION
+	 * Authorization} header based on the given username and password
+	 * suppliers. Meant to be used in combination with
+	 * {@link org.springframework.web.reactive.function.client.WebClient.RequestHeadersSpec#headers(java.util.function.Consumer)}.
+	 * <p>Note that Basic Authentication only supports characters in the
+	 * {@linkplain StandardCharsets#ISO_8859_1 ISO-8859-1} character set.
+	 *
+	 * @param usernameSupplier supplier for the username
+	 * @param passwordSupplier supplier for the password
+	 * @return a consumer that adds a Basic Authentication header
+	 */
+	public static Consumer<HttpHeaders> basicAuthenticationConsumer(Supplier<String> usernameSupplier,
+			Supplier<String> passwordSupplier) {
+
+		Assert.notNull(usernameSupplier, "Username Supplier must not be null");
+		Assert.notNull(passwordSupplier, "Password Supplier must not be null");
+
+		return new BasicAuthenticationConsumer(usernameSupplier, passwordSupplier);
+	}
+
+
+	/**
+	 * @see #basicAuthenticationConsumer
+	 */
+	private static class BasicAuthenticationConsumer implements Consumer<HttpHeaders> {
+
+		private final Supplier<String> usernameSupplier;
+
+		private final Supplier<String> passwordSupplier;
+
+		public BasicAuthenticationConsumer(Supplier<String> usernameSupplier,
+				Supplier<String> passwordSupplier) {
+			this.usernameSupplier = usernameSupplier;
+			this.passwordSupplier = passwordSupplier;
+		}
+
+		@Override
+		public void accept(HttpHeaders httpHeaders) {
+			String username = this.usernameSupplier.get();
+			String password = this.passwordSupplier.get();
+
+			Assert.state(username != null, "Supplied username is null");
+			Assert.state(password != null, "Supplied password is null");
+
+			checkIllegalCharacters(username, password);
+
+			String credentialsString = username + ":" + password;
+			byte[] credentialBytes = credentialsString.getBytes(StandardCharsets.ISO_8859_1);
+			byte[] encodedBytes = Base64.getEncoder().encode(credentialBytes);
+			String encodedCredentials = new String(encodedBytes, StandardCharsets.ISO_8859_1);
+
+			httpHeaders.set(HttpHeaders.AUTHORIZATION, "Basic " + encodedCredentials);
+		}
+
+		private static void checkIllegalCharacters(String username, String password) {
+			// Basic authentication only supports ISO 8859-1
+			CharsetEncoder encoder = StandardCharsets.ISO_8859_1.newEncoder();
+			if (!encoder.canEncode(username) || !encoder.canEncode(password)) {
+				throw new IllegalArgumentException(
+						"Username or password contains characters that cannot be encoded to ISO-8859-1");
+			}
+		}
+
+	}
 }