You could also use it to generate code automatically, for clients that communicate with your API. For example, frontend, mobile or IoT applications.

## Recap, step by step { #recap-step-by-step }

### Step 1: import `FastAPI` { #step-1-import-fastapi }

{* ../../docs_src/first_steps/tutorial001.py hl[1] *}

`FastAPI` is a Python class that provides all the functionality for your API.

# 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**.

        include:
          - os: windows-latest
            java: 21
            root-pom: pom.xml
    runs-on: ${{ matrix.os }}
    env:
      ROOT_POM: ${{ matrix.root-pom }}
    steps:
      # Cancel any previous runs for the same branch that are still running.
      - name: 'Cancel previous runs'
        uses: styfle/cancel-workflow-action@85880fa0301c86cca9da44039ee3bb12d3bedbfa # 0.12.1
        with:

    ///

    The `--upgrade` option tells `pip` to upgrade the packages if they are already installed.

    Because the previous step copying the file could be detected by the **Docker cache**, this step will also **use the Docker cache** when available.

    init: GradleBuildStep.() -> Unit,
    custom: GradleBuildStep.() -> Unit,
): GradleBuildStep =
    GradleBuildStep(init)
        .apply(custom)
        .also {
            step(it)
        }

/**
 * Adds a [Gradle build step](https://confluence.jetbrains.com/display/TCDL/Gradle)
 * that runs with the Gradle wrapper.
 *
 * @see GradleBuildStep
 */
fun BuildSteps.gradleWrapper(
    buildType: BuildType? = null,

* Share database connections.
* Enforce security, authentication, role requirements, etc.
* And many other things...

All these, while minimizing code repetition.

## First Steps { #first-steps }

Let's see a very simple example. It will be so simple that it is not very useful, for now.

But this way we can focus on how the **Dependency Injection** system works.

        title: '${{ github.event.inputs.release_branch }} cherry-pick: ${{ steps.cherrypick.outputs.SHORTSHA }} "${{ steps.cherrypick.outputs.TITLE }}"'
        committer: TensorFlow Release Automation <******@****.***>
        token: ${{ secrets.JENKINS_TOKEN }}
        base: ${{ github.event.inputs.release_branch }}
        branch: ${{ github.event.inputs.release_branch }}-${{ steps.cherrypick.outputs.SHORTSHA }}
        reviewers: learning-to-play

{* ../../docs_src/security/tutorial005_an_py310.py hl[5,9,13,47,65,106,108:116,122:126,130:136,141,157] *}

Now let's review those changes step by step.

## OAuth2 Security scheme { #oauth2-security-scheme }

The first change is that now we are declaring the OAuth2 security scheme with two available scopes, `me` and `items`.

      - run: ./gradlew compileAll -DdisableLocalCache=true ${{ steps.determine-sys-prop-args.outputs.sys-prop-args }}
      - uses: actions/upload-artifact@v4
        if: always()
        with:
          name: build-receipt.properties
          path: platforms/core-runtime/base-services/build/generated-resources/build-receipt/org/gradle/build-receipt.properties
    outputs:
      matrix: ${{ steps.setup-matrix.outputs.matrix }}

jobs:
  publish:
    runs-on: ubuntu-latest
    if: github.repository == 'square/okhttp' && github.ref == 'refs/heads/master'

    steps:
      - name: Checkout
        uses: actions/checkout@v5

      - name: Configure JDK
        uses: actions/setup-java@v5
        with:
          distribution: 'zulu'
          java-version: 11