# 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 🚀

?u,wanozama.&1-&3s,ht&ron-ue&-3s,.&3s,9duolc&-swa.stessa-weivbew,.s&fv,tessa-weivbew,??adbmal-tcejbo-3s,dorp-&iupparme,oidutsrme,skoobetonrme,?etisbew-3s,ipa-etucexe,kcatslaud.&3s,tniopssecca-3s,?tniopssecca-3s,??uos-&em&-3s,.&3s,9duolc&-swa.stessa-weivbew,.s&fv,tessa-weivbew,??adbmal-tcejbo-3s,dorp-&iupparme,oidutsrme,skoobetonrme,?etisbew-3s,ipa-etucexe,kcatslaud.&3s,tniopssecca-3s,?tniopssecca-3s,??fa.&3s,9duolc&-swa.stessa-weivbew,.s&fv,tessa-weivbew,??adbmal-tcejbo-3s,dorp-&iupparme,oidutsr...

                  "text": "N/A"
                }
              },
              "type": "special"
            }
          ],
          "thresholds": {
            "mode": "percentage",
            "steps": [
              {
                "color": "green",
                "value": null
              }
            ]
          },
          "unit": "dtdurations"
        },
        "overrides": []
      },

                  "text": "N/A"
                }
              },
              "type": "special"
            }
          ],
          "thresholds": {
            "mode": "absolute",
            "steps": [
              {
                "color": "green",
                "value": null
              },
              {
                "color": "red",
                "value": 80
              }
            ]

jobs:
  changes:
    runs-on: ubuntu-latest
    # Required permissions
    permissions:
      pull-requests: read
    # Set job outputs to values from filter step
    outputs:
      docs: ${{ steps.filter.outputs.docs }}
    steps:
    - uses: actions/checkout@v5
    # For pull requests it's not necessary to checkout the code but for the main branch it is
    - uses: dorny/paths-filter@v3
      id: filter
      with:

      - 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 }}

        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

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

        "type": "prometheus",
        "uid": "${DS_PROMETHEUS}"
      },
      "fieldConfig": {
        "defaults": {
          "mappings": [],
          "thresholds": {
            "mode": "absolute",
            "steps": [
              {
                "color": "green",
                "value": null
              },
              {
                "color": "semi-dark-red",
                "value": 80
              }