Use MIME decoder to read OAuth2 resource server public key

Fixes gh-16624

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/oauth2/resource/reactive/ReactiveOAuth2ResourceServerJwkConfiguration.java

@@ -68,8 +68,8 @@ class ReactiveOAuth2ResourceServerJwkConfiguration {
 
 	private byte[] getKeySpec(String keyValue) {
 		keyValue = keyValue.replace("-----BEGIN PUBLIC KEY-----", "")
-				.replace("-----END PUBLIC KEY-----", "").replace("\n", "");
+				.replace("-----END PUBLIC KEY-----", "");
-		return Base64.getDecoder().decode(keyValue);
+		return Base64.getMimeDecoder().decode(keyValue);
 	}
 
 	@Bean

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/security/oauth2/resource/servlet/OAuth2ResourceServerJwtConfiguration.java

@@ -70,8 +70,8 @@ class OAuth2ResourceServerJwtConfiguration {
 
 	private byte[] getKeySpec(String keyValue) {
 		keyValue = keyValue.replace("-----BEGIN PUBLIC KEY-----", "")
-				.replace("-----END PUBLIC KEY-----", "").replace("\n", "");
+				.replace("-----END PUBLIC KEY-----", "");
-		return Base64.getDecoder().decode(keyValue);
+		return Base64.getMimeDecoder().decode(keyValue);
 	}
 
 	@Bean