Helper script for getting git credentials from the environment (#1190)

Useful for passing in fine-grained personal access tokens via environment variables when SSHing
into a node so that they don't have to be stored in a shared environment.

apps/git/git-credential-from-env.py

@@ -0,0 +1,60 @@
+#!/usr/bin/env python3
+#
+# Credential helper to enable people to store fine grained access tokens in ssh environment
+# variables for use on a shared instance.
+# git config --global credential.helper ..../git-credentials-from-env.py
+# git config --global credential.useHttpPath true
+#
+# To make a fine grained access token:
+# Github console upper right -> Settings -> Developer settings (lower left)
+#   -> Personal access tokens -> Fine-grained tokens -> Generate new token
+#
+# You will likely need to change the resource owner to your organization.
+# After selecting a repository, make sure to set the right repository permisisons
+# To push and pull you will need Contents = Read and write; and Metadata = Read-only
+#
+# Get the token to the remote machine, you can
+# 1. gpg encrypt it, mail it and decrypt it; or
+# 2. type it in manually. To verify correct typing, use a checksum.
+#    linux: sha256sum <file
+#    windows: certutil -hashfile file SHA256
+
+import sys
+import logging
+import os
+
+if len(sys.argv) != 2 or sys.argv[1] != "get":
+    exit(0)
+
+d = {}
+
+for line in sys.stdin:
+    if line == "\n":
+        break
+    p = line.rstrip().split("=")  # Fix the missing split
+    if len(p) != 2:
+        logging.error(f"{__file__}: unable to parse {line}")
+        continue
+    d[p[0]] = p[1]
+
+if d.get("host", "") == "github.com" and "aryn-ai" in d.get("path", ""):
+    assert "ARYN_GITHUB_USER" in os.environ
+    assert "ARYN_GITHUB_KEY" in os.environ
+    print("protocol=https")
+    print("host=github.com")
+    print(f"username={os.environ['ARYN_GITHUB_USER']}")
+    print(f"password={os.environ['ARYN_GITHUB_KEY']}")
+    logging.error(f"git-credentials-from-env helper: Aryn github.com was used for {d['path']}")
+    exit(0)
+
+if "CUSTOMER_USER" in os.environ and "CUSTOMER_KEY" in os.environ:
+    print("protocol=https")
+    print("host=github.com")
+    print(f"username={os.environ['CUSTOMER_USER']}")
+    print(f"password={os.environ['CUSTOMER_KEY']}")
+    logging.error(f"git-credentials-from-env helper: Customer user was used for {d['path']}")
+    exit(0)
+
+logging.error(f"WARNING from {__file__}: Unable to find CUSTOMER_USER and CUSTOMER_KEY in environ.")
+logging.error("WARNING since the helper was enabled, this is probably an error.")
+exit(0)