How to fix 401 Unauthorized when I use the AWS SDK with Cloudflare R2 Storage in Spring Boot example?

I have a problem about fixing 401 Unauthorized issue when I upload a file through Cloudflare R2 Storage in my Spring Boot example.

I get Token value, access key, secret key and jurisdiction-specific endpoints for S3 clients from Account API Tokens of R2 Storage.

Bucket name is stored in Eastern Europe (EEUR)

Here are the dependencies defined in pom.xml:

    <dependency>
        <groupId>software.amazon.awssdk</groupId>
        <artifactId>s3</artifactId>
        <version>${cloudflare-aws-sdk-version}</version>
        <scope>compile</scope>
    </dependency>

    <!-- AWS SDK’s Apache HTTP-client integration -->
    <dependency>
        <groupId>software.amazon.awssdk</groupId>
        <artifactId>apache-client</artifactId>
        <version>${cloudflare-aws-sdk-version}</version>
    </dependency>

    <!-- force the httpclient version to 4.5.13 -->
    <dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>httpclient</artifactId>
        <version>${apache-httpclient.version}</version>
    </dependency>

Here is the application.yml file:

cloudflare:
  r2:
    endpoint: https://<account-id>.r2.cloudflarestorage.com
    accessKey: access-key
    secretKey: secret-key
    bucket: buckey-name

Here is the CloudflareProperties class:

@Getter
@Setter
@ConfigurationProperties(prefix = "cloudflare.r2")
public class CloudflareProperties {
    private String endpoint;
    private String accessKey;
    private String secretKey;
}

This is the CloudflareR2Config class:

@Configuration
@EnableConfigurationProperties(CloudflareProperties.class)
@RequiredArgsConstructor
public class CloudflareR2Config {

    private final CloudflareProperties cloudflareProperties;

    @Bean
    public S3Client s3Client() {

        return S3Client.builder()
                .httpClientBuilder(ApacheHttpClient.builder())
                .region(Region.of("eeur"))
                .endpointOverride(URI.create(cloudflareProperties.getEndpoint()))
                .credentialsProvider(StaticCredentialsProvider.create(
                        AwsBasicCredentials.create(
                                cloudflareProperties.getAccessKey(),
                                cloudflareProperties.getSecretKey())))
                .serviceConfiguration(S3Configuration.builder().pathStyleAccessEnabled(true).build())
                .build();
    }

}

And this is the service class:

@Service
@RequiredArgsConstructor
public class MediaService {

    private final S3Client s3Client;

    @Value("${cloudflare.r2.bucket}")
    private String bucket;

    public String uploadFile(MultipartFile file) {

        String originalFilename = Optional.ofNullable(file.getOriginalFilename())
                .orElseThrow(() -> new UnsupportedMediaTypeException("Filename is missing"))
                .toLowerCase();

        String contentType = Optional.ofNullable(file.getContentType())
                .orElseThrow(() -> new UnsupportedMediaTypeException("Content-Type is unknown"));

        String folder = switch (getFileExtension(originalFilename)) {
            case "jpg", "jpeg", "png" -> "images";
            case "mp4", "mov" -> "videos";
            default -> throw new UnsupportedMediaTypeException("Unsupported file type: " + contentType);
        };

        String key = folder + "/" + UUID.randomUUID() + "-" + originalFilename;

        PutObjectRequest putRequest = PutObjectRequest.builder()
                .bucket(bucket)
                .key(key)
                .contentType(contentType)
                .build();

        try {
            s3Client.putObject(putRequest, RequestBody.fromBytes(file.getBytes()));
        } catch (IOException e) {
            throw new FileUploadException("File upload to Cloudflare R2 failed", e);
        }

        return key;
    }


    private String getFileExtension(String filename) {
        int lastDot = filename.lastIndexOf('.');
        if (lastDot == -1 || lastDot == filename.length() - 1) {
            throw new IllegalArgumentException("Invalid file extension in filename: " + filename);
        }
        return filename.substring(lastDot + 1);
    }
}

This is the controller class:

@RestController
@RequiredArgsConstructor
@RequestMapping("/api/media")
public class MediaController {

    private final MediaService mediaService;

    @PostMapping("/upload")
    public ResponseEntity<String> uploadImage(@RequestParam("file") MultipartFile file) {

        String key = mediaService.uploadFile(file);
        return ResponseEntity.ok(key);
    }
}

When I send a request to localhost:7777/api/media/upload, I got this error:

{
    "error": "Internal Server Error",
    "message": "Unauthorized (Service: S3, Status Code: 401, Request ID: null) (SDK Attempt Count: 1)"
}

How can I fix the issue?