# 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**.

### 1. Fetch the root identity

his voice, and, with tears running down his cheeks, he went on
again:--

  `You may not have lived much under the sea--' (`I haven't,' said Alice)--
`and perhaps you were never even introduced to a lobster--'
(Alice began to say `I once tasted--' but checked herself hastily,
and said `No, never') `--so you can have no idea what a delightful
thing a Lobster Quadrille is!'

  private val readyAsyncCalls = ArrayDeque<AsyncCall>()

  /** Running asynchronous calls. Includes canceled calls that haven't finished yet. */
  private val runningAsyncCalls = ArrayDeque<AsyncCall>()

  /** Running synchronous calls. Includes canceled calls that haven't finished yet. */
  private val runningSyncCalls = ArrayDeque<RealCall>()

  constructor(executorService: ExecutorService) : this() {

      /** Iterate a copy of the entries to defend against concurrent modification errors. */
      private val delegate = ArrayList(lruEntries.values).iterator()

      /** The snapshot to return from [next]. Null if we haven't computed that yet. */
      private var nextSnapshot: Snapshot? = null

      /** The snapshot to remove with [remove]. Null if removal is illegal. */
      private var removeSnapshot: Snapshot? = null

But you still need to use `Path` for the `item_id` path parameter. And you don't want to use `Annotated` for some reason.

Python will complain if you put a value with a "default" before a value that doesn't have a "default".

But you can re-order them, and have the value without a default (the query parameter `q`) first.

        return true
      }
    }

    // If we have a routes left, use 'em.
    if (routeSelection?.hasNext() == true) return true

    // If we haven't initialized the route selector yet, assume it'll have at least one route.
    val localRouteSelector = routeSelector ?: return true

    // If we do have a route selector, use its routes.
    return localRouteSelector.hasNext()
  }

  /**

    <module>maven-artifact-test</module>
    <module>maven-core</module>
    <module>maven-error-diagnostics</module>
    <module>maven-model</module>
    <module>maven-monitor</module>
    <module>maven-plugin-api</module>
    <module>maven-plugin-descriptor</module>
    <module>maven-plugin-parameter-documenter</module>
    <module>maven-plugin-registry</module>
    <module>maven-plugin-tools</module>
    <module>maven-profile</module>

    </plugins>
  </reporting>

  <scm>
    <connection>scm:svn:http://svn.apache.org/repos/asf/maven/pom/maven/tags/maven-parent-4</connection>
    <developerConnection>scm:svn:https://svn.apache.org/repos/asf/maven/pom/maven/tags/maven-parent-4</developerConnection>
    <url>http://svn.apache.org/viewvc/maven/pom/maven/tags/maven-parent-4</url>
  </scm>

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>maven-test</groupId>
  <artifactId>maven-test-c</artifactId>
  <packaging>jar</packaging>
  <version>1.0</version>