isSvcAccForRequestor := false
	if targetUser == requestorUser || targetUser == requestorParentUser {
		isSvcAccForRequestor = true
	}

	var (
		targetGroups []string
		err          error
	)

	// If we are creating svc account for request sender, ensure that targetUser
	// is a real user (i.e. not derived credentials).
	if isSvcAccForRequestor {
		if requestorIsDerivedCredential {

 * that exhibits the problem.
 *
 */
public interface Problem {

    /**
     * The different severity levels for a problem, in decreasing order.
     */
    enum Severity {
        FATAL, //
        ERROR, //
        WARNING //
    }

    /**
     * Gets the hint about the source of the problem. While the syntax of this hint is unspecified and depends on the

                        c = interpolator.interpolate(value, recursionInterceptor);
                    } catch (InterpolationException e) {
                        problems.add(new ModelProblemCollectorRequest(Severity.ERROR, Version.BASE)
                                .setMessage(e.getMessage())
                                .setException(e));
                    }
                    cache.put(value, c);
                }

 * bytes in length.
 *
 * The cache stores its data in a directory on the filesystem. This directory must be exclusive to
 * the cache; the cache may delete or overwrite files from its directory. It is an error for
 * multiple processes to use the same cache directory at the same time.
 *
 * This cache limits the number of bytes that it will store on the filesystem. When the number of

  /** True if there was an exception on the connection to the peer. */
  internal var hasFailure: Boolean = false
    private set

  internal val connection: RealConnection
    get() = codec.carrier as? RealConnection ?: error("no connection for CONNECT tunnels")

  internal val isCoalescedConnection: Boolean
    get() = finder.routePlanner.address.url.host != codec.carrier.route.address.url.host

  @Throws(IOException::class)

{!> ../../docs_src/security/tutorial007.py!}
```

////

这类似于：

```Python
if not (credentials.username == "stanleyjobson") or not (credentials.password == "swordfish"):
    # Return some error
    ...
```

但使用 `secrets.compare_digest()`，可以防御**时差攻击**，更加安全。

### 时差攻击

什么是**时差攻击**？

假设攻击者试图猜出用户名与密码。

他们发送用户名为 `johndoe`，密码为 `love123`  的请求。

然后，Python 代码执行如下操作：

# This should only be necessary when running on A GCP VM, on a default
# network, which has the MTU of 1460,
# due to 40 bytes being reserved for GCP's internal usage.
# Note, an invalid sub-interface name will lead to an obscure error, e.g.:
# "The filename, directory name, or volume label syntax is incorrect."
# In such cases, check that the name of the sub-interface is valid:
# `netsh interface show interface`

        try {
            updateRepositoryMetadata(localRepository, remoteRepository);
        } catch (IOException | XMLStreamException e) {
            throw new RepositoryMetadataStoreException("Error updating group repository metadata", e);
        }
    }

    protected void updateRepositoryMetadata(ArtifactRepository localRepository, ArtifactRepository remoteRepository)

	hstats.totalS3Requests.Inc(api)
	code := w.StatusCode

	switch {
	case code == 0:
	case code == 499:
		// 499 is a good error, shall be counted as canceled.
		hstats.totalS3Canceled.Inc(api)
	case code >= http.StatusBadRequest:
		if code >= http.StatusInternalServerError {
			hstats.totalS35xxErrors.Inc(api)
		} else {

/**
Do not use this class. Writing to the OutputStream of this type of socket
requires leaving a 4 byte prefix for the NBT header. IOW you must call
write( buf, 4, len ). Calling write( buf, 0, len ) will generate an error.
 */

public class NbtSocket extends Socket {

    private static final int SSN_SRVC_PORT = 139;
    private static final int BUFFER_SIZE = 512;
    private static final int DEFAULT_SO_TIMEOUT = 5000;