Add client credentials authentication filter

Fixes gh-5

core/src/main/java/org/springframework/security/oauth2/server/authorization/authentication/OAuth2ClientAuthenticationToken.java

@@ -44,11 +44,11 @@ public class OAuth2ClientAuthenticationToken extends AbstractAuthenticationToken
 
 	@Override
 	public Object getCredentials() {
-		return null;
+		return this.clientSecret;
 	}
 
 	@Override
 	public Object getPrincipal() {
-		return null;
+		return this.clientId;
 	}
 }

samples/boot/minimal/spring-authorization-server-samples-boot-minimal.gradle

@@ -4,6 +4,7 @@ dependencies {
 	implementation 'org.springframework.boot:spring-boot-starter-web'
 	implementation 'org.springframework.boot:spring-boot-starter-security'
 	implementation 'com.nimbusds:oauth2-oidc-sdk'
+	implementation project(':spring-authorization-server-core')
 
 	testImplementation('org.springframework.boot:spring-boot-starter-test') {
 		exclude group: 'org.junit.vintage', module: 'junit-vintage-engine'

samples/boot/minimal/src/main/java/sample/ClientCredentialsAuthenticationFilter.java

@@ -0,0 +1,103 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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 sample;
+
+import org.springframework.http.HttpMethod;
+import org.springframework.security.authentication.AuthenticationManager;
+import org.springframework.security.authentication.BadCredentialsException;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.security.oauth2.server.authorization.authentication.OAuth2ClientAuthenticationToken;
+import org.springframework.security.web.util.matcher.AntPathRequestMatcher;
+import org.springframework.security.web.util.matcher.RequestMatcher;
+import org.springframework.web.filter.OncePerRequestFilter;
+
+import javax.servlet.FilterChain;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.util.Base64;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+/**
+ * A filter to perform client authentication for the Token Endpoint.
+ *
+ * See <a href="https://tools.ietf.org/html/rfc6749#section-2.3.1">RFC-6749 2.3.1</a>.
+ */
+public class ClientCredentialsAuthenticationFilter extends OncePerRequestFilter {
+	private final AuthenticationManager authenticationManager;
+	private final RequestMatcher requestMatcher = new AntPathRequestMatcher("/oauth2/token", HttpMethod.POST.name());
+
+	public ClientCredentialsAuthenticationFilter(AuthenticationManager authenticationManager) {
+		this.authenticationManager = authenticationManager;
+	}
+
+	@Override
+	protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain)
+			throws ServletException, IOException {
+
+		if (this.requestMatcher.matches(request)) {
+			String[] credentials = extractBasicAuthenticationCredentials(request);
+			String clientId = credentials[0];
+			String clientSecret = credentials[1];
+
+			OAuth2ClientAuthenticationToken authenticationToken = new OAuth2ClientAuthenticationToken(clientId, clientSecret);
+
+			Authentication authentication = this.authenticationManager.authenticate(authenticationToken);
+
+			SecurityContextHolder.getContext().setAuthentication(authentication);
+		}
+
+		chain.doFilter(request, response);
+	}
+
+	private String[] extractBasicAuthenticationCredentials(HttpServletRequest request) {
+		String header = request.getHeader("Authorization");
+		if (header != null && header.toLowerCase().startsWith("basic ")) {
+			return extractAndDecodeHeader(header, request);
+		}
+		throw new BadCredentialsException("Missing basic authentication header");
+	}
+
+	// Taken from BasicAuthenticationFilter (spring-security-web)
+	private String[] extractAndDecodeHeader(String header, HttpServletRequest request) {
+
+		byte[] base64Token = header.substring(6).getBytes(UTF_8);
+		byte[] decoded;
+		try {
+			decoded = Base64.getDecoder().decode(base64Token);
+		}
+		catch (IllegalArgumentException e) {
+			throw new BadCredentialsException("Failed to decode basic authentication token");
+		}
+
+		String token = new String(decoded, getCredentialsCharset(request));
+
+		int delim = token.indexOf(":");
+
+		if (delim == -1) {
+			throw new BadCredentialsException("Invalid basic authentication token");
+		}
+		return new String[] { token.substring(0, delim), token.substring(delim + 1) };
+	}
+
+	protected Charset getCredentialsCharset(HttpServletRequest httpRequest) {
+		return UTF_8;
+	}
+}

samples/boot/minimal/src/test/java/sample/ClientCredentialsAuthenticationFilterTests.java

@@ -0,0 +1,113 @@
+/*
+ * Copyright 2020 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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 sample;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.springframework.mock.web.MockFilterChain;
+import org.springframework.mock.web.MockHttpServletRequest;
+import org.springframework.mock.web.MockHttpServletResponse;
+import org.springframework.mock.web.MockServletContext;
+import org.springframework.security.authentication.AuthenticationManager;
+import org.springframework.security.authentication.BadCredentialsException;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.security.oauth2.server.authorization.authentication.OAuth2ClientAuthenticationToken;
+import org.springframework.util.Assert;
+
+import static java.net.URI.create;
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static java.util.Base64.getEncoder;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.post;
+
+public class ClientCredentialsAuthenticationFilterTests {
+	private static final String CLIENT_ID = "myclientid";
+	private static final String CLIENT_SECRET = "myclientsecret";
+	private final AuthenticationManager authenticationManager = authentication -> {
+		Assert.isInstanceOf(OAuth2ClientAuthenticationToken.class, authentication);
+		OAuth2ClientAuthenticationToken token = (OAuth2ClientAuthenticationToken) authentication;
+		if (CLIENT_ID.equals(token.getPrincipal()) && CLIENT_SECRET.equals(token.getCredentials())) {
+			authentication.setAuthenticated(true);
+			return authentication;
+		}
+		throw new BadCredentialsException("Bad credentials");
+	};
+	private final ClientCredentialsAuthenticationFilter filter = new ClientCredentialsAuthenticationFilter(this.authenticationManager);
+
+	@BeforeEach
+	public void setup() {
+		SecurityContextHolder.clearContext();
+	}
+
+	@Test
+	public void doFilterWhenUrlDoesNotMatchThenDontAuthenticate() throws Exception {
+		MockHttpServletRequest request = post(create("/someotherendpoint")).buildRequest(new MockServletContext());
+		request.addHeader("Authorization", basicAuthHeader(CLIENT_ID, CLIENT_SECRET));
+
+		filter.doFilter(request, new MockHttpServletResponse(), new MockFilterChain());
+
+		assertThat(SecurityContextHolder.getContext().getAuthentication()).isNull();
+	}
+
+	@Test
+	public void doFilterWhenRequestMatchesThenAuthenticate() throws Exception {
+		MockHttpServletRequest request = post(create("/oauth2/token")).buildRequest(new MockServletContext());
+		request.addHeader("Authorization", basicAuthHeader(CLIENT_ID, CLIENT_SECRET));
+
+		filter.doFilter(request, new MockHttpServletResponse(), new MockFilterChain());
+
+		assertThat(SecurityContextHolder.getContext().getAuthentication().isAuthenticated()).isTrue();
+	}
+
+	@Test
+	public void doFilterWhenBasicAuthenticationHeaderIsMissingThenThrowBadCredentialsException() {
+		MockHttpServletRequest request = post(create("/oauth2/token")).buildRequest(new MockServletContext());
+		assertThatExceptionOfType(BadCredentialsException.class).isThrownBy(() ->
+				filter.doFilter(request, new MockHttpServletResponse(), new MockFilterChain()));
+	}
+
+	@Test
+	public void doFilterWhenBasicAuthenticationHeaderHasInvalidSyntaxThenThrowBadCredentialsException() {
+		MockHttpServletRequest request = post(create("/oauth2/token")).buildRequest(new MockServletContext());
+		request.addHeader("Authorization", "Basic invalid");
+
+		assertThatExceptionOfType(BadCredentialsException.class).isThrownBy(() ->
+				filter.doFilter(request, new MockHttpServletResponse(), new MockFilterChain()));
+	}
+
+	@Test
+	public void doFilterWhenBasicAuthenticationProvidesIncorrectSecretThenThrowBadCredentialsException() {
+		MockHttpServletRequest request = post(create("/oauth2/token")).buildRequest(new MockServletContext());
+		request.addHeader("Authorization", basicAuthHeader(CLIENT_ID, "incorrectsecret"));
+
+		assertThatExceptionOfType(BadCredentialsException.class).isThrownBy(() ->
+				filter.doFilter(request, new MockHttpServletResponse(), new MockFilterChain()));
+	}
+
+	@Test
+	public void doFilterWhenBasicAuthenticationProvidesIncorrectClientIdThenThrowBadCredentialsException() {
+		MockHttpServletRequest request = post(create("/oauth2/token")).buildRequest(new MockServletContext());
+		request.addHeader("Authorization", basicAuthHeader("anotherclientid", CLIENT_SECRET));
+
+		assertThatExceptionOfType(BadCredentialsException.class).isThrownBy(() ->
+				filter.doFilter(request, new MockHttpServletResponse(), new MockFilterChain()));
+	}
+
+	private static String basicAuthHeader(String clientId, String clientSecret) {
+		return "Basic " + getEncoder().encodeToString((clientId + ":" + clientSecret).getBytes(UTF_8));
+	}
+}