Add OAuth 2 client library for Python

.env.example

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+# Copy to .env and fill in the required values. Never commit .env or key files.
+CLIENT_ID=
+KID=
+TOKEN_ENDPOINT=https://sandbox.api.mastercard.com/oauth/token
+ISSUER=https://sandbox.api.mastercard.com
+API_BASE_URL=https://sandbox.api.mastercard.com/oauth2-petstore/petstore
+SCOPES=
+
+# GitHub Actions uses PRIVATE_KEY with PEM content. For local runs, prefer
+# PRIVATE_KEY_PATH pointing to an existing key file. Do not copy private keys
+# into this Git checkout.
+PRIVATE_KEY=
+PRIVATE_KEY_PATH=
+PRIVATE_KEY_PASSWORD=
+
+# Optional network settings.
+SSL_CA_CERT=
+GATEWAY_HTTPS_PROXY=

.github/workflows/ci-aiohttp.yml

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+name: aiohttp
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches:
+      - '**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    name: aiohttp ${{ matrix.label }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - label: minimum
+            aiohttp: 'aiohttp==3.13.0'
+          - label: latest
+            aiohttp: aiohttp
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: '3.11'
+          cache: pip
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -e . --group dev "${{ matrix.aiohttp }}"
+          python -m pip check
+
+      - name: Run direct aiohttp unit tests
+        run: python -m pytest -v tests/unit/direct/aiohttp
+
+      - name: Run direct aiohttp integration tests
+        run: python -m pytest -v tests/integration/direct/aiohttp

.github/workflows/ci-httpx.yml

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+name: HTTPX
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches:
+      - '**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    name: HTTPX ${{ matrix.label }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - label: minimum
+            httpx: 'httpx==0.28.0'
+          - label: latest
+            httpx: httpx
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: '3.11'
+          cache: pip
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -e . --group dev "${{ matrix.httpx }}"
+          python -m pip check
+
+      - name: Run direct HTTPX unit tests
+        run: python -m pytest -v tests/unit/direct/httpx
+
+      - name: Run direct HTTPX integration tests
+        run: python -m pytest -v tests/integration/direct/httpx

.github/workflows/ci-openapi-asyncio.yml

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+name: OpenAPI asyncio
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches:
+      - '**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    name: OpenAPI asyncio ${{ matrix.label }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - label: minimum
+            aiohttp: 'aiohttp==3.13.0'
+          - label: latest
+            aiohttp: aiohttp
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: '3.11'
+          cache: pip
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -e . --group dev --group generator "${{ matrix.aiohttp }}"
+          python -m pip check
+
+      - name: Generate OpenAPI asyncio test client
+        run: python scripts/generate_test_clients.py --client asyncio
+
+      - name: Run OpenAPI asyncio unit tests
+        run: python -m pytest -v tests/unit/openapi/asyncio
+
+      - name: Run OpenAPI asyncio integration tests
+        run: python -m pytest -v tests/integration/openapi/asyncio

.github/workflows/ci-openapi-httpx.yml

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+name: OpenAPI HTTPX
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches:
+      - '**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    name: OpenAPI HTTPX ${{ matrix.label }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - label: minimum
+            httpx: 'httpx==0.28.0'
+          - label: latest
+            httpx: httpx
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: '3.11'
+          cache: pip
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -e . --group dev --group generator "${{ matrix.httpx }}"
+          python -m pip check
+
+      - name: Generate OpenAPI HTTPX test client
+        run: python scripts/generate_test_clients.py --client httpx
+
+      - name: Run OpenAPI HTTPX unit tests
+        run: python -m pytest -v tests/unit/openapi/httpx
+
+      - name: Run OpenAPI HTTPX integration tests
+        run: python -m pytest -v tests/integration/openapi/httpx

.github/workflows/ci-openapi.yml

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+name: OpenAPI Generator
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches:
+      - '**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  generated-clients:
+    name: OpenAPI Generator ${{ matrix['generator-version'] }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        generator-version:
+          - '7.23.0'
+          - '7.24.0'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: '3.14'
+          cache: pip
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -e . --group dev "openapi-generator-cli[jdk4py]==${{ matrix['generator-version'] }}"
+          python -m pip check
+
+      - name: Generate all OpenAPI test clients
+        run: python scripts/generate_test_clients.py
+
+      - name: Run OpenAPI unit tests
+        run: python -m pytest -v tests/unit/openapi
+
+      - name: Run OpenAPI integration tests
+        run: python -m pytest -v tests/integration/openapi

.github/workflows/ci-python.yml

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+name: Python
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches:
+      - '**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    name: Python ${{ matrix['python-version'] }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - python-version: '3.11'
+            cryptography: 'cryptography==45.0.1'
+          - python-version: '3.12'
+            cryptography: 'cryptography==45.0.1'
+          - python-version: '3.13'
+            cryptography: cryptography
+          - python-version: '3.14'
+            cryptography: cryptography
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Python ${{ matrix['python-version'] }}
+        uses: actions/setup-python@v6
+        with:
+          python-version: ${{ matrix['python-version'] }}
+          cache: pip
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -e . --group dev "${{ matrix.cryptography }}"
+          python -m pip check
+
+      - name: Run unit tests
+        run: python -m pytest -v tests/unit/test_*.py tests/unit/direct
+
+      - name: Run direct integration tests
+        run: python -m pytest -v tests/integration/direct

.github/workflows/ci-requests.yml

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+name: Requests
+
+on:
+  push:
+    branches:
+      - '**'
+  pull_request:
+    branches:
+      - '**'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  tests:
+    name: Requests ${{ matrix.label }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - label: minimum
+            requests: 'requests==2.33.0'
+          - label: latest
+            requests: requests
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v5
+
+      - name: Set up Python
+        uses: actions/setup-python@v6
+        with:
+          python-version: '3.11'
+          cache: pip
+
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install -e . --group dev "${{ matrix.requests }}"
+          python -m pip check
+
+      - name: Run Requests unit tests
+        run: python -m pytest -v tests/unit/direct/requests
+
+      - name: Run Requests integration tests
+        run: python -m pytest -v tests/integration/direct/requests