},
        "german_keywords": {

# Security - First Steps { #security-first-steps }

Let's imagine that you have your **backend** API in some domain.

And you have a **frontend** in another domain or in a different path of the same domain (or in a mobile application).

And you want to have a way for the frontend to authenticate with the backend, using a **username** and **password**.

We can use **OAuth2** to build that with **FastAPI**.

# First Steps { #first-steps }

The simplest FastAPI file could look like this:

{* ../../docs_src/first_steps/tutorial001.py *}

Copy that to a file `main.py`.

Run the live server:

<div class="termy">

```console
$ <font color="#4E9A06">fastapi</font> dev <u style="text-decoration-style:solid">main.py</u>

  <span style="background-color:#009485"><font color="#D3D7CF"> FastAPI </font></span>  Starting development server 🚀

  @Override
  public UnmodifiableIterator<C> descendingIterator() {
    return new AbstractSequentialIterator<C>(last()) {
      final C first = first();

      @Override
      protected @Nullable C computeNext(C previous) {
        return equalsOrThrow(previous, first) ? null : domain.previous(previous);
      }
    };
  }

   * the first are ignored.
   */
  public static <E> ImmutableSet<E> of(E e1, E e2, E e3, E e4, E e5) {
    return new RegularSetBuilderImpl<E>(5).add(e1).add(e2).add(e3).add(e4).add(e5).review().build();
  }

  /**
   * Returns an immutable set containing the given elements, minus duplicates, in the order each was

 * offering expected O(n + k log k) performance (worst case O(n log k)) for n calls to {@link
 * #offer} and a call to {@link #topK}, with O(k) memory. In comparison, quickselect has the same
 * asymptotics but requires O(n) memory, and a {@code PriorityQueue} implementation takes O(n log
 * k). In benchmarks, this implementation performs at least as well as either implementation, and
 * degrades more gracefully for worst-case input.
 *

    int len = sequence.length();
    int first;
    int last;

    for (first = 0; first < len; first++) {
      if (!matches(sequence.charAt(first))) {
        break;
      }
    }
    for (last = len - 1; last > first; last--) {
      if (!matches(sequence.charAt(last))) {
        break;
      }
    }

    return sequence.subSequence(first, last + 1).toString();
  }

  /**

		t.Fatalf("Failed to commit, got error %v", err)
	}

	if err := DB.First(&User{}, "name = ?", user.Name).Error; err != nil {
		t.Fatalf("Should find saved record")
	}

	if err := DB.First(&User{}, "name = ?", user1.Name).Error; err == nil {
		t.Fatalf("Should not find rollbacked record")
	}

	if err := DB.First(&User{}, "name = ?", user2.Name).Error; err != nil {
		t.Fatalf("Should find saved record")
	}

          node.setNext(oldHead);
          if (casWaiters(oldHead, node)) {
            while (true) {
              OverflowAvoidingLockSupport.parkNanos(this, remainingNanos);
              // Check interruption first, if we woke up due to interruption we need to honor that.
              if (Thread.interrupted()) {
                removeWaiter(node);
                throw new InterruptedException();
              }

		}
		lastUpdatedAt = n
	}

	checkOtherData := func(name string) {
		var first, last User
		if err := DB.Where("id = ?", users[0].ID).First(&first).Error; err != nil {
			t.Errorf("errors happened when query before user: %v", err)
		}
		CheckUser(t, first, *users[0])

		if err := DB.Where("id = ?", users[2].ID).First(&last).Error; err != nil {
			t.Errorf("errors happened when query after user: %v", err)
		}