But first, let's check some small concepts.

## In a hurry?

If you don't care about any of these terms and you just need to add security with authentication based on username and password *right now*, skip to the next chapters.

## OAuth2

OAuth2 is a specification that defines several ways to handle authentication and authorization.

It is quite an extensive specification and covers several complex use cases.

    }.test();
  }

  public void testIteratorNoSuchElementException() {
    Iterator<E> iterator = collection.iterator();
    while (iterator.hasNext()) {
      iterator.next();
    }

    assertThrows(NoSuchElementException.class, () -> iterator.next());
  }

$(function() {
  $('input[type="text"],select,textarea', ".login-box,section.content")
    .first()
    .focus();
  $(".form-group .has-error")
    .first()
    .next("input,select,textarea")
    .focus();

  $("section.content input").keypress(function(e) {
    var $submitButton;
    if (e.which === 13) {
      $submitButton = $("input#submit, button#submit");
      if ($submitButton.length > 0) {
        $submitButton[0].submit();
      }

class Item:
    name: str
    price: float
    tags: List[str] = field(default_factory=list)
    description: Union[str, None] = None
    tax: Union[float, None] = None


app = FastAPI()


@app.get("/items/next", response_model=Item)
async def read_next_item():
    return {
        "name": "Island In The Moon",
        "price": 12.99,
        "description": "A place to be playin' and havin' fun",
        "tags": ["breater"],

    /**
     * @return the expiration time of this entry
     */
    long getExpiration ();


    /**
     * 
     * @return pointer to next referral, points to self if there is no further referral
     */
    DfsReferralData next ();


    /**
     * @return the link
     */
    String getLink ();

            return i < array.length;
          }

          @Override
          public String next() {
            if (!hasNext()) {
              throw new NoSuchElementException();
            }
            return array[i++];
          }
        };

    assertTrue(iterator.hasNext());
    assertEquals("a", iterator.next());
    assertThrows(UnsupportedOperationException.class, () -> iterator.remove());
  }

import java.util.function.Function;
import java.util.function.Supplier;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Tester for {@code Spliterator} implementations.
 *
 * @since NEXT (but since 21.0 in the JRE flavor)
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
@SuppressWarnings("Java7ApiChecker")
@IgnoreJRERequirement // Users will use this only if they're already using Spliterator.

  }

  @CollectionFeature.Require({SUPPORTS_ADD, FAILS_FAST_ON_CONCURRENT_MODIFICATION})
  public void testSetCountZeroToOneConcurrentWithEntrySetIteration() {
    Iterator<Entry<E>> iterator = getMultiset().entrySet().iterator();
    assertSetCount(e3(), 1);
    assertThrows(ConcurrentModificationException.class, () -> iterator.next());
  }

    }

    @Override
    public boolean hasNext() {
      return !stack.isEmpty();
    }

    @Override
    public T next() {
      Iterator<T> itr = stack.getLast(); // throws NSEE if empty
      T result = checkNotNull(itr.next());
      if (!itr.hasNext()) {
        stack.removeLast();
      }
      Iterator<T> childItr = children(result).iterator();
      if (childItr.hasNext()) {

                if( sort == 0 ) {
                    if( compareNames( dirents[i], name, (SmbFile)iter.next() ) < 0 ) {
                        break;
                    }
                } else if( sort == 1 ) {
                    if( compareSizes( dirents[i], name, (SmbFile)iter.next() ) < 0 ) {
                        break;
                    }
                } else if( sort == 2 ) {