Fix to save all values for multi-valued request parameters

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2AuthorizationCodeAuthenticationConverter.java

@@ -84,7 +84,7 @@ public Authentication convert(HttpServletRequest request) {
 					!key.equals(OAuth2ParameterNames.CLIENT_ID) &&
 					!key.equals(OAuth2ParameterNames.CODE) &&
 					!key.equals(OAuth2ParameterNames.REDIRECT_URI)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2AuthorizationCodeRequestAuthenticationConverter.java

@@ -138,7 +138,7 @@ public Authentication convert(HttpServletRequest request) {
 					!key.equals(OAuth2ParameterNames.REDIRECT_URI) &&
 					!key.equals(OAuth2ParameterNames.SCOPE) &&
 					!key.equals(OAuth2ParameterNames.STATE)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2AuthorizationConsentAuthenticationConverter.java

@@ -93,7 +93,7 @@ public Authentication convert(HttpServletRequest request) {
 			if (!key.equals(OAuth2ParameterNames.CLIENT_ID) &&
 					!key.equals(OAuth2ParameterNames.STATE) &&
 					!key.equals(OAuth2ParameterNames.SCOPE)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2ClientCredentialsAuthenticationConverter.java

@@ -79,7 +79,7 @@ public Authentication convert(HttpServletRequest request) {
 		parameters.forEach((key, value) -> {
 			if (!key.equals(OAuth2ParameterNames.GRANT_TYPE) &&
 					!key.equals(OAuth2ParameterNames.SCOPE)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2DeviceAuthorizationConsentAuthenticationConverter.java

@@ -110,7 +110,7 @@ public Authentication convert(HttpServletRequest request) {
 					!key.equals(OAuth2ParameterNames.USER_CODE) &&
 					!key.equals(OAuth2ParameterNames.STATE) &&
 					!key.equals(OAuth2ParameterNames.SCOPE)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2DeviceAuthorizationRequestAuthenticationConverter.java

@@ -75,7 +75,7 @@ public Authentication convert(HttpServletRequest request) {
 		parameters.forEach((key, value) -> {
 			if (!key.equals(OAuth2ParameterNames.CLIENT_ID) &&
 					!key.equals(OAuth2ParameterNames.SCOPE)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2DeviceCodeAuthenticationConverter.java

@@ -74,7 +74,7 @@ public Authentication convert(HttpServletRequest request) {
 			if (!key.equals(OAuth2ParameterNames.GRANT_TYPE) &&
 					!key.equals(OAuth2ParameterNames.CLIENT_ID) &&
 					!key.equals(OAuth2ParameterNames.DEVICE_CODE)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2DeviceVerificationAuthenticationConverter.java

@@ -80,7 +80,7 @@ public Authentication convert(HttpServletRequest request) {
 		Map<String, Object> additionalParameters = new HashMap<>();
 		parameters.forEach((key, value) -> {
 			if (!key.equals(OAuth2ParameterNames.USER_CODE)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2EndpointUtils.java

@@ -16,8 +16,8 @@
 package org.springframework.security.oauth2.server.authorization.web.authentication;
 
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.Map;
+import java.util.stream.Collectors;
 
 import jakarta.servlet.http.HttpServletRequest;
 
@@ -59,11 +59,13 @@ static Map<String, Object> getParametersIfMatchesAuthorizationCodeGrantRequest(H
 		if (!matchesAuthorizationCodeGrantRequest(request)) {
 			return Collections.emptyMap();
 		}
-		Map<String, Object> parameters = new HashMap<>(getParameters(request).toSingleValueMap());
+		MultiValueMap<String, String> parameters = getParameters(request);
 		for (String exclusion : exclusions) {
 			parameters.remove(exclusion);
 		}
-		return parameters;
+		return parameters.entrySet().stream()
+			.collect(Collectors.toMap(Map.Entry::getKey,
+				e -> e.getValue().size() == 1 ? e.getValue().get(0) : e.getValue().toArray(new String[0])));
 	}
 
 	static boolean matchesAuthorizationCodeGrantRequest(HttpServletRequest request) {

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2RefreshTokenAuthenticationConverter.java

@@ -90,7 +90,7 @@ public Authentication convert(HttpServletRequest request) {
 			if (!key.equals(OAuth2ParameterNames.GRANT_TYPE) &&
 					!key.equals(OAuth2ParameterNames.REFRESH_TOKEN) &&
 					!key.equals(OAuth2ParameterNames.SCOPE)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2TokenIntrospectionAuthenticationConverter.java

@@ -69,7 +69,7 @@ public Authentication convert(HttpServletRequest request) {
 		parameters.forEach((key, value) -> {
 			if (!key.equals(OAuth2ParameterNames.TOKEN) &&
 					!key.equals(OAuth2ParameterNames.TOKEN_TYPE_HINT)) {
-				additionalParameters.put(key, value.get(0));
+				additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
 			}
 		});
 

oauth2-authorization-server/src/main/java/org/springframework/security/oauth2/server/authorization/web/authentication/PublicClientAuthenticationConverter.java

@@ -16,6 +16,7 @@
 package org.springframework.security.oauth2.server.authorization.web.authentication;
 
 import java.util.HashMap;
+import java.util.Map;
 
 import jakarta.servlet.http.HttpServletRequest;
 
@@ -68,7 +69,12 @@ public Authentication convert(HttpServletRequest request) {
 
 		parameters.remove(OAuth2ParameterNames.CLIENT_ID);
 
+		Map<String, Object> additionalParameters = new HashMap<>();
+		parameters.forEach((key, value) -> {
+			additionalParameters.put(key, value.size() == 1 ? value.get(0) : value.toArray(new String[0]));
+		});
+
 		return new OAuth2ClientAuthenticationToken(clientId, ClientAuthenticationMethod.NONE, null,
-				new HashMap<>(parameters.toSingleValueMap()));
+				additionalParameters);
 	}
 }

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/OAuth2AuthorizationEndpointFilterTests.java

@@ -589,6 +589,8 @@ public void doFilterWhenAuthorizationRequestAuthenticatedThenAuthorizationRespon
 				.thenReturn(authorizationCodeRequestAuthenticationResult);
 
 		MockHttpServletRequest request = createAuthorizationRequest(registeredClient);
+		request.addParameter("foo", "value1", "value2");
+
 		MockHttpServletResponse response = new MockHttpServletResponse();
 		FilterChain filterChain = mock(FilterChain.class);
 
@@ -603,6 +605,12 @@ public void doFilterWhenAuthorizationRequestAuthenticatedThenAuthorizationRespon
 				.asInstanceOf(type(WebAuthenticationDetails.class))
 				.extracting(WebAuthenticationDetails::getRemoteAddress)
 				.isEqualTo(REMOTE_ADDRESS);
+
+		// Assert that multi-valued request parameters are preserved
+		assertThat(authorizationCodeRequestAuthenticationCaptor.getValue().getAdditionalParameters())
+				.extracting(ap -> ap.get("foo"))
+				.asInstanceOf(type(String[].class))
+				.isEqualTo(new String[] { "value1", "value2" });
 		assertThat(response.getStatus()).isEqualTo(HttpStatus.FOUND.value());
 		assertThat(response.getRedirectedUrl()).isEqualTo(
 				"https://example.com?param=encoded%20parameter%20value&code=code&state=client%20state");

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/OAuth2DeviceAuthorizationEndpointFilterTests.java

@@ -195,6 +195,7 @@ public void doFilterWhenDeviceAuthorizationRequestThenDeviceAuthorizationRespons
 
 		MockHttpServletRequest request = createRequest();
 		request.addParameter("custom-param-1", "custom-value-1");
+		request.addParameter("custom-param-2", "custom-value-2a", "custom-value-2b");
 		MockHttpServletResponse response = new MockHttpServletResponse();
 		FilterChain filterChain = mock(FilterChain.class);
 		this.filter.doFilter(request, response, filterChain);
@@ -211,7 +212,8 @@ public void doFilterWhenDeviceAuthorizationRequestThenDeviceAuthorizationRespons
 		assertThat(deviceAuthorizationRequestAuthentication.getPrincipal()).isEqualTo(clientPrincipal);
 		assertThat(deviceAuthorizationRequestAuthentication.getScopes()).isEmpty();
 		assertThat(deviceAuthorizationRequestAuthentication.getAdditionalParameters())
-				.containsExactly(entry("custom-param-1", "custom-value-1"));
+				.containsExactly(entry("custom-param-1", "custom-value-1"),
+					entry("custom-param-2", new String[] { "custom-value-2a", "custom-value-2b" }));
 		// @formatter:off
 		assertThat(deviceAuthorizationRequestAuthentication.getDetails())
 				.asInstanceOf(type(WebAuthenticationDetails.class))

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/OAuth2DeviceVerificationEndpointFilterTests.java

@@ -187,6 +187,7 @@ public void doFilterWhenDeviceAuthorizationConsentRequestThenSuccess() throws Ex
 		request.addParameter(OAuth2ParameterNames.STATE, STATE);
 		request.addParameter(OAuth2ParameterNames.USER_CODE, USER_CODE);
 		request.addParameter("custom-param-1", "custom-value-1");
+		request.addParameter("custom-param-2", "custom-value-2a", "custom-value-2b");
 		MockHttpServletResponse response = new MockHttpServletResponse();
 		FilterChain filterChain = mock(FilterChain.class);
 		this.filter.doFilter(request, response, filterChain);
@@ -207,7 +208,7 @@ public void doFilterWhenDeviceAuthorizationConsentRequestThenSuccess() throws Ex
 		assertThat(deviceAuthorizationConsentAuthentication.getUserCode()).isEqualTo(USER_CODE);
 		assertThat(deviceAuthorizationConsentAuthentication.getScopes()).containsExactly("scope-1", "scope-2");
 		assertThat(deviceAuthorizationConsentAuthentication.getAdditionalParameters())
-				.containsExactly(entry("custom-param-1", "custom-value-1"));
+				.containsExactly(entry("custom-param-1", "custom-value-1"), entry("custom-param-2", new String[]{ "custom-value-2a", "custom-value-2b" }));
 	}
 
 	@Test

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/OAuth2TokenEndpointFilterTests.java

@@ -273,7 +273,8 @@ public void doFilterWhenAuthorizationCodeTokenRequestThenAccessTokenResponse() t
 		assertThat(authorizationCodeAuthentication.getRedirectUri()).isEqualTo(
 				request.getParameter(OAuth2ParameterNames.REDIRECT_URI));
 		assertThat(authorizationCodeAuthentication.getAdditionalParameters())
-				.containsExactly(entry("custom-param-1", "custom-value-1"));
+				.containsExactly(entry("custom-param-1", "custom-value-1"),
+					entry("custom-param-2", new String[]{ "custom-value-2a", "custom-value-2b" }));
 		assertThat(authorizationCodeAuthentication.getDetails())
 				.asInstanceOf(type(WebAuthenticationDetails.class))
 				.extracting(WebAuthenticationDetails::getRemoteAddress)
@@ -340,7 +341,8 @@ public void doFilterWhenClientCredentialsTokenRequestThenAccessTokenResponse() t
 		assertThat(clientCredentialsAuthentication.getPrincipal()).isEqualTo(clientPrincipal);
 		assertThat(clientCredentialsAuthentication.getScopes()).isEqualTo(registeredClient.getScopes());
 		assertThat(clientCredentialsAuthentication.getAdditionalParameters())
-				.containsExactly(entry("custom-param-1", "custom-value-1"));
+				.containsExactly(entry("custom-param-1", "custom-value-1"),
+					entry("custom-param-2", new String[]{ "custom-value-2a", "custom-value-2b" }));
 		assertThat(clientCredentialsAuthentication.getDetails())
 				.asInstanceOf(type(WebAuthenticationDetails.class))
 				.extracting(WebAuthenticationDetails::getRemoteAddress)
@@ -430,7 +432,8 @@ public void doFilterWhenRefreshTokenRequestThenAccessTokenResponse() throws Exce
 		assertThat(refreshTokenAuthenticationToken.getPrincipal()).isEqualTo(clientPrincipal);
 		assertThat(refreshTokenAuthenticationToken.getScopes()).isEqualTo(registeredClient.getScopes());
 		assertThat(refreshTokenAuthenticationToken.getAdditionalParameters())
-				.containsExactly(entry("custom-param-1", "custom-value-1"));
+				.containsExactly(entry("custom-param-1", "custom-value-1"),
+					entry("custom-param-2", new String[]{ "custom-value-2a", "custom-value-2b" }));
 		assertThat(refreshTokenAuthenticationToken.getDetails())
 				.asInstanceOf(type(WebAuthenticationDetails.class))
 				.extracting(WebAuthenticationDetails::getRemoteAddress)
@@ -613,6 +616,7 @@ private static MockHttpServletRequest createAuthorizationCodeTokenRequest(Regist
 		// The client does not need to send the client ID param, but we are resilient in case they do
 		request.addParameter(OAuth2ParameterNames.CLIENT_ID, registeredClient.getClientId());
 		request.addParameter("custom-param-1", "custom-value-1");
+		request.addParameter("custom-param-2", "custom-value-2a", "custom-value-2b");
 
 		return request;
 	}
@@ -627,6 +631,7 @@ private static MockHttpServletRequest createClientCredentialsTokenRequest(Regist
 		request.addParameter(OAuth2ParameterNames.SCOPE,
 				StringUtils.collectionToDelimitedString(registeredClient.getScopes(), " "));
 		request.addParameter("custom-param-1", "custom-value-1");
+		request.addParameter("custom-param-2", "custom-value-2a", "custom-value-2b");
 
 		return request;
 	}
@@ -642,6 +647,7 @@ private static MockHttpServletRequest createRefreshTokenTokenRequest(RegisteredC
 		request.addParameter(OAuth2ParameterNames.SCOPE,
 				StringUtils.collectionToDelimitedString(registeredClient.getScopes(), " "));
 		request.addParameter("custom-param-1", "custom-value-1");
+		request.addParameter("custom-param-2", "custom-value-2a", "custom-value-2b");
 
 		return request;
 	}

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/OAuth2TokenIntrospectionEndpointFilterTests.java

@@ -219,7 +219,7 @@ public void doFilterWhenTokenIntrospectionRequestValidThenSuccessResponse() thro
 		MockHttpServletRequest request = createTokenIntrospectionRequest(
 				accessToken.getTokenValue(), OAuth2TokenType.ACCESS_TOKEN.getValue());
 		request.addParameter("custom-param-1", "custom-value-1");
-		request.addParameter("custom-param-2", "custom-value-2");
+		request.addParameter("custom-param-2", "custom-value-2a", "custom-value-2b");
 
 		MockHttpServletResponse response = new MockHttpServletResponse();
 		FilterChain filterChain = mock(FilterChain.class);
@@ -236,7 +236,7 @@ public void doFilterWhenTokenIntrospectionRequestValidThenSuccessResponse() thro
 		assertThat(tokenIntrospectionAuthentication.getValue().getAdditionalParameters())
 				.contains(
 						entry("custom-param-1", "custom-value-1"),
-						entry("custom-param-2", "custom-value-2"));
+						entry("custom-param-2", new String[]{"custom-value-2a", "custom-value-2b"}));
 
 		OAuth2TokenIntrospection tokenIntrospectionResponse = readTokenIntrospectionResponse(response);
 		assertThat(tokenIntrospectionResponse.isActive()).isEqualTo(tokenClaims.isActive());

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/authentication/ClientSecretBasicAuthenticationConverterTests.java

@@ -106,6 +106,7 @@ public void convertWhenAuthorizationHeaderBasicWithValidCredentialsThenReturnCli
 	@Test
 	public void convertWhenConfidentialClientWithPkceParametersThenAdditionalParametersIncluded() throws Exception {
 		MockHttpServletRequest request = createPkceTokenRequest();
+		request.addParameter("custom-param-1", "custom-value-1a", "custom-value-1b");
 		request.addHeader(HttpHeaders.AUTHORIZATION, "Basic " + encodeBasicAuth("clientId", "secret"));
 		OAuth2ClientAuthenticationToken authentication = (OAuth2ClientAuthenticationToken) this.converter.convert(request);
 		assertThat(authentication.getPrincipal()).isEqualTo("clientId");
@@ -115,7 +116,8 @@ public void convertWhenConfidentialClientWithPkceParametersThenAdditionalParamet
 				.containsOnly(
 						entry(OAuth2ParameterNames.GRANT_TYPE, AuthorizationGrantType.AUTHORIZATION_CODE.getValue()),
 						entry(OAuth2ParameterNames.CODE, "code"),
-						entry(PkceParameterNames.CODE_VERIFIER, "code-verifier-1"));
+						entry(PkceParameterNames.CODE_VERIFIER, "code-verifier-1"),
+						entry("custom-param-1", new String[] { "custom-value-1a", "custom-value-1b" }));
 	}
 
 	private static String encodeBasicAuth(String clientId, String secret) throws Exception {

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/authentication/ClientSecretPostAuthenticationConverterTests.java

@@ -95,6 +95,7 @@ public void convertWhenConfidentialClientWithPkceParametersThenAdditionalParamet
 		MockHttpServletRequest request = createPkceTokenRequest();
 		request.addParameter(OAuth2ParameterNames.CLIENT_ID, "client-1");
 		request.addParameter(OAuth2ParameterNames.CLIENT_SECRET, "client-secret");
+		request.addParameter("custom-param-1", "custom-value-1a", "custom-value-1b");
 		OAuth2ClientAuthenticationToken authentication = (OAuth2ClientAuthenticationToken) this.converter.convert(request);
 		assertThat(authentication.getPrincipal()).isEqualTo("client-1");
 		assertThat(authentication.getCredentials()).isEqualTo("client-secret");
@@ -103,7 +104,8 @@ public void convertWhenConfidentialClientWithPkceParametersThenAdditionalParamet
 				.containsOnly(
 						entry(OAuth2ParameterNames.GRANT_TYPE, AuthorizationGrantType.AUTHORIZATION_CODE.getValue()),
 						entry(OAuth2ParameterNames.CODE, "code"),
-						entry(PkceParameterNames.CODE_VERIFIER, "code-verifier-1"));
+						entry(PkceParameterNames.CODE_VERIFIER, "code-verifier-1"),
+						entry("custom-param-1", new String[] { "custom-value-1a", "custom-value-1b" }));
 	}
 
 	private static MockHttpServletRequest createPkceTokenRequest() {

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/authentication/JwtClientAssertionAuthenticationConverterTests.java

@@ -107,14 +107,18 @@ public void convertWhenJwtAssertionThenReturnClientAuthenticationToken() {
 		request.addParameter(OAuth2ParameterNames.CLIENT_ID, "client-1");
 		request.addParameter(OAuth2ParameterNames.GRANT_TYPE, AuthorizationGrantType.AUTHORIZATION_CODE.getValue());
 		request.addParameter(OAuth2ParameterNames.CODE, "code");
+		request.addParameter("custom-param-1", "custom-value-1");
+		request.addParameter("custom-param-2", "custom-value-2a", "custom-value-2b");
 		OAuth2ClientAuthenticationToken authentication = (OAuth2ClientAuthenticationToken) this.converter.convert(request);
 		assertThat(authentication.getPrincipal()).isEqualTo("client-1");
 		assertThat(authentication.getCredentials()).isEqualTo("jwt-assertion");
 		assertThat(authentication.getClientAuthenticationMethod().getValue()).isEqualTo(JWT_BEARER_TYPE);
 		assertThat(authentication.getAdditionalParameters())
 				.containsOnly(
 						entry(OAuth2ParameterNames.GRANT_TYPE, AuthorizationGrantType.AUTHORIZATION_CODE.getValue()),
-						entry(OAuth2ParameterNames.CODE, "code"));
+						entry(OAuth2ParameterNames.CODE, "code"),
+						entry("custom-param-1", "custom-value-1"),
+						entry("custom-param-2", new String[] {"custom-value-2a", "custom-value-2b"}));
 	}
 
 	private void assertThrown(MockHttpServletRequest request, String errorCode) {

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2DeviceAuthorizationConsentAuthenticationConverterTests.java

@@ -246,7 +246,7 @@ public void convertWhenAllParametersThenReturnDeviceAuthorizationConsentAuthenti
 		request.addParameter(OAuth2ParameterNames.SCOPE, "message.read");
 		request.addParameter(OAuth2ParameterNames.SCOPE, "message.write");
 		request.addParameter("param-1", "value-1");
-		request.addParameter("param-2", "value-2");
+		request.addParameter("param-2", "value-2", "value-2b");
 
 		SecurityContextImpl securityContext = new SecurityContextImpl();
 		securityContext.setAuthentication(new TestingAuthenticationToken("user", null));
@@ -261,7 +261,8 @@ public void convertWhenAllParametersThenReturnDeviceAuthorizationConsentAuthenti
 		assertThat(authentication.getUserCode()).isEqualTo(USER_CODE);
 		assertThat(authentication.getScopes()).containsExactly("message.read", "message.write");
 		assertThat(authentication.getAdditionalParameters())
-				.containsExactly(entry("param-1", "value-1"), entry("param-2", "value-2"));
+				.containsExactly(entry("param-1", "value-1"),
+					entry("param-2", new String[]{"value-2", "value-2b"}));
 	}
 
 	@Test

oauth2-authorization-server/src/test/java/org/springframework/security/oauth2/server/authorization/web/authentication/OAuth2DeviceAuthorizationRequestAuthenticationConverterTests.java

@@ -95,7 +95,7 @@ public void convertWhenAllParametersThenReturnDeviceAuthorizationRequestAuthenti
 		request.addParameter(OAuth2ParameterNames.CLIENT_ID, CLIENT_ID);
 		request.addParameter(OAuth2ParameterNames.SCOPE, "message.read message.write");
 		request.addParameter("param-1", "value-1");
-		request.addParameter("param-2", "value-2");
+		request.addParameter("param-2", "value-2", "value-2b");
 
 		SecurityContextImpl securityContext = new SecurityContextImpl();
 		securityContext.setAuthentication(new TestingAuthenticationToken(CLIENT_ID, null));
@@ -108,7 +108,8 @@ public void convertWhenAllParametersThenReturnDeviceAuthorizationRequestAuthenti
 		assertThat(authentication.getAuthorizationUri()).endsWith(AUTHORIZATION_URI);
 		assertThat(authentication.getScopes()).containsExactly("message.read", "message.write");
 		assertThat(authentication.getAdditionalParameters())
-				.containsExactly(entry("param-1", "value-1"), entry("param-2", "value-2"));
+				.containsExactly(entry("param-1", "value-1"),
+					entry("param-2", new String[]{"value-2", "value-2b"}));
 	}
 
 	private static MockHttpServletRequest createRequest() {