fix: explicitly declare support for Python 3.13

.kokoro/samples/python3.13/common.cfg

@@ -0,0 +1,37 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Specify which tests to run
+env_vars: {
+    key: "RUN_TESTS_SESSION"
+    value: "unit-3.13"
+}
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Download resources for system tests (service account key, etc.)
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/google-auth-library-python"
+
+# Use the trampoline script to run in docker.
+build_file: "google-auth-library-python/.kokoro/trampoline.sh"
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-multi"
+}
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/google-auth-library-python/.kokoro/build.sh"
+}
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/google-auth-library-python/.kokoro/samples-test-setup.sh"
+}

.kokoro/samples/python3.13/continuous.cfg

@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}

.kokoro/samples/python3.13/periodic-head.cfg

@@ -0,0 +1,11 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/google-auth-library-python/.kokoro/test-samples-against-head.sh"
+}

.kokoro/samples/python3.13/periodic.cfg

@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "False"
+}

.kokoro/samples/python3.13/presubmit.cfg

@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}

CONTRIBUTING.rst

@@ -19,7 +19,7 @@ A few notes on making changes to ``google-auth-library-python``.
   using ``nox -s docs``.
 
 - The change must work fully on the following CPython versions:
-  3.7, 3.8, 3.9, 3.10, 3.11 and 3.12 across macOS, Linux, and Windows.
+  3.7, 3.8, 3.9, 3.10, 3.11, 3.12 and 3.13 across macOS, Linux, and Windows.
 
 - The codebase *must* have 100% test statement coverage after each commit.
   You can test coverage via ``nox -e cover``.

noxfile.py

@@ -84,7 +84,7 @@ def mypy(session):
     session.run("mypy", "-p", "google", "-p", "tests", "-p", "tests_async")
 
 
-@nox.session(python=["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"])
+@nox.session(python=["3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"])
 def unit(session):
     constraints_path = str(
         CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"

samples/cloud-client/snippets/noxfile.py

@@ -60,7 +60,7 @@
 ]
 
 
-@nox.session(python=["3.7", "3.8", "3.9", "3.10", "3.11", "3.12"])
+@nox.session(python=["3.7", "3.8", "3.9", "3.10", "3.11", "3.12", "3.13"])
 def unit(session):
     # constraints_path = str(
     #     CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"

setup.py

@@ -72,6 +72,7 @@
         "Programming Language :: Python :: 3.10",
         "Programming Language :: Python :: 3.11",
         "Programming Language :: Python :: 3.12",
+        "Programming Language :: Python :: 3.13",
         "Development Status :: 5 - Production/Stable",
         "Intended Audience :: Developers",
         "License :: OSI Approved :: Apache Software License",