想像你有一個部署在某個網域的後端 API。

還有一個前端在另一個網域，或同一網域的不同路徑（或是行動應用程式）。

你希望前端能用使用者名稱與密碼向後端進行身分驗證。

我們可以用 OAuth2 搭配 FastAPI 來實作。

但不必通讀整份冗長規格只為了找出你需要的幾個重點。

就用 FastAPI 提供的工具處理安全性。

## 看起來如何 { #how-it-looks }

先直接跑範例看效果，再回頭理解其原理。

## 建立 `main.py` { #create-main-py }

將範例複製到檔案 `main.py`：

{* ../../docs_src/security/tutorial001_an_py310.py *}

## 執行 { #run-it }

/// info

而**前端**在另一个域名，或同一域名的不同路径（或在移动应用中）。

你希望前端能通过**username** 和 **password** 与后端进行身份验证。

我们可以用 **OAuth2** 在 **FastAPI** 中实现它。

但为了节省你的时间，不必为获取少量信息而通读冗长的规范。

我们直接使用 **FastAPI** 提供的安全工具。

## 效果预览 { #how-it-looks }

先直接运行代码看看效果，之后再回过头理解其背后的原理。

## 创建 `main.py` { #create-main-py }

把下面的示例代码复制到 `main.py`：

{* ../../docs_src/security/tutorial001_an_py310.py *}

## 运行 { #run-it }

/// info | 信息

    public @Nullable Entry<K, V> firstEntry() {
      return standardFirstEntry();
    }

    /*
     * We can't override lastEntry to delegate to standardLastEntry, as it would create an infinite
     * loop. Instead, we test standardLastEntry manually below.
     */

    @Override
    public @Nullable Entry<K, V> pollFirstEntry() {
      return standardPollFirstEntry();
    }

    @Override

   */
  private static long fullFingerprint(byte[] bytes, int offset, int length) {
    // For lengths over 64 bytes we hash the end first, and then as we
    // loop we keep 56 bytes of state: v, w, x, y, and z.
    long x = load64(bytes, offset);
    long y = load64(bytes, offset + length - 16) ^ K1;
    long z = load64(bytes, offset + length - 56) ^ K0;
    long[] v = new long[2];

      }
    };

    abstract Map<Element, Element> create(Collection<Element> contents);
  }

  @Param({"5", "50", "500", "5000", "50000"})
  private int size;

  // TODO: look at exact (==) hits vs. equals() hits?
  @Param("0.9")
  private double hitRate;

  @Param("true")
  private boolean isUserTypeFast;

  // "" means no fixed seed
  @Param("")

	// Keys returns a slice of all cache keys in the store.
	Keys() []string

	// Get retrieves a Stmt object from the store based on the given key.
	// Parameters:
	//   key: The key used to look up the Stmt object.
	// Returns:
	//   *Stmt: The found Stmt object, or nil if not found.
	//   bool: Indicates whether the corresponding Stmt object was successfully found.
	Get(key string) (*Stmt, bool)

	newtierfi.TransitionStatus = ""
	newtierfi.SetTierFreeVersionID(fvIDs[1])
	report()
	_, err = xl.DeleteVersion(newtierfi)
	report()
	fatalErr(err)

	// At this point the version stack must look as below,
	// v3 --> free version      00000000-0000-0000-0000-0000000000f2 (from removal of null version)
	// v2 --> free version      00000000-0000-0000-0000-0000000000f1 (from overwriting of null version )

    this.allowsParallelEdges = allowsParallelEdges;
    return this;
  }

  /**
   * Specifies whether the network will allow self-loops (edges that connect a node to itself).
   * Attempting to add a self-loop to a network that does not allow them will throw an {@link
   * UnsupportedOperationException}.
   *
   * <p>The default value is {@code false}.
   */
  @CanIgnoreReturnValue

    }

    @Test
    @DisplayName("connection and failure status delegate to transport")
    void testConnectionAndFailureStatus() {
        SmbSessionImpl session = newSession();

        // Make session look connected via setSessionSetup
        Smb2SessionSetupResponse resp = mock(Smb2SessionSetupResponse.class);
        when(resp.getSessionId()).thenReturn(42L);
        session.setSessionSetup(resp);

		return hex.EncodeToString(sum256[:])
	}

	var (
		defaultSha256Cksum string
		v                  []string
		ok                 bool
	)

	// For a presigned request we look at the query param for sha256.
	if isRequestPresignedSignatureV4(r) {
		// X-Amz-Content-Sha256, if not set in presigned requests, checksum
		// will default to 'UNSIGNED-PAYLOAD'.
		defaultSha256Cksum = unsignedPayload