```

</div>

////

This information will be useful when learning about [Virtual Environments](virtual-environments.md){.internal-link target=_blank}.

## Conclusion

With this you should have a basic understanding of what **environment variables** are and how to use them in Python.

// StorageErr represents error generated by xlStorage call.
type StorageErr string

func (h StorageErr) Error() string {
	return string(h)
}

// Collection of basic errors.
var baseErrs = []error{
	errDiskNotFound,
	errFaultyDisk,
	errFaultyRemoteDisk,
}

var baseIgnoredErrs = baseErrs

// Is a one place function which converts all os.PathError

    contentSchema: Optional["SchemaOrBool"] = None
    # Ref: JSON Schema Validation 2020-12: https://json-schema.org/draft/2020-12/json-schema-validation.html#name-a-vocabulary-for-basic-meta
    # A Vocabulary for Basic Meta-Data Annotations
    title: Optional[str] = None
    description: Optional[str] = None
    default: Optional[Any] = None
    deprecated: Optional[bool] = None
    readOnly: Optional[bool] = None

    public static final String INDEXING_TARGET = "indexingTarget";

    public static final String NUM_OF_THREADS = "numOfThreads";

    public static final String BASIC = "BASIC";

    public static final String DIGEST = "DIGEST";

    public static final String NTLM = "NTLM";

    public static final String FORM = "FORM";

    public static final String SAMBA = "SAMBA";

        headers = headersOf("www-authenticate", "Basic realm=\"protected area\""),
        body = "Please authenticate.",
      ),
    )
    server.enqueue(
      MockResponse(body = "Successful auth!"),
    )
    val credential = basic("username", "password")
    client =
      client.newBuilder()
        .authenticator(RecordingOkAuthenticator(credential, "Basic"))
        .build()

Use `Response.challenges()` to get the schemes and realms of any authentication challenges. When fulfilling a `Basic` challenge, use `Credentials.basic(username, password)` to encode the request header.

=== ":material-language-kotlin: Kotlin"
    ```kotlin
      private val client = OkHttpClient.Builder()

		},
		config.HelpKV{
			Key:         target.ElasticUsername,
			Description: "username for Elasticsearch basic-auth",
			Optional:    true,
			Type:        "string",
			Sensitive:   true,
		},
		config.HelpKV{
			Key:         target.ElasticPassword,
			Description: "password for Elasticsearch basic-auth",
			Optional:    true,
			Type:        "string",
			Sensitive:   true,
			Secret:      true,
		},

 * based on these entries.
 * <p>
 * To fully understand the information exposed by this class a description
 * of the access check algorithm used by Windows is required. The following
 * is a basic description of the algorithm. For a more complete description
 * we recommend reading the section on Access Control in Keith Brown's
 * "The .NET Developer's Guide to Windows Security" (which is also
 * available online).
 * <p>

OpenAPI 定义了以下安全方案：

* `apiKey`：一个特定于应用程序的密钥，可以来自：
    * 查询参数。
    * 请求头。
    * cookie。
* `http`：标准的 HTTP 身份认证系统，包括：
    * `bearer`: 一个值为 `Bearer` 加令牌字符串的 `Authorization` 请求头。这是从 OAuth2 继承的。
    * HTTP Basic 认证方式。
    * HTTP Digest，等等。
* `oauth2`：所有的 OAuth2 处理安全性的方式（称为「流程」）。
    *以下几种流程适合构建 OAuth 2.0 身份认证的提供者（例如 Google，Facebook，Twitter，GitHub 等）：
        * `implicit`
        * `clientCredentials`
        * `authorizationCode`

// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package etag

import (
	"context"
	"crypto/md5"
	"fmt"
	"hash"
	"io"
)

// Tagger is the interface that wraps the basic ETag method.
type Tagger interface {
	ETag() ETag
}

type wrapReader struct {
	io.Reader
	Tagger
}

var _ Tagger = wrapReader{} // compiler check

// ETag returns the ETag of the underlying Tagger.