Initial commit of microsign FunctionApp

[alextserepov]

Initial Commit: Microsign Service

This version enables anonymous signature verification only. Access to Key Vault functionality is managed through Key Vault access policies via managed identity. Only the permission for signature verification should be granted.

[henrirosten]

Consider fixing relevant pylint errors (you decide if they are relevant or not):

❯ pylint ~/projects/ci-yubi/microsign/function_app.py
************* Module function_app
ci-yubi/microsign/function_app.py:15:50: C0303: Trailing whitespace (trailing-whitespace)
ci-yubi/microsign/function_app.py:16:91: C0303: Trailing whitespace (trailing-whitespace)
ci-yubi/microsign/function_app.py:40:0: C0301: Line too long (103/100) (line-too-long)
ci-yubi/microsign/function_app.py:48:0: C0301: Line too long (109/100) (line-too-long)
ci-yubi/microsign/function_app.py:1:0: C0114: Missing module docstring (missing-module-docstring)
ci-yubi/microsign/function_app.py:17:0: C0116: Missing function or method docstring (missing-function-docstring)
ci-yubi/microsign/function_app.py:45:11: W0718: Catching too general exception Exception (broad-exception-caught)
ci-yubi/microsign/function_app.py:25:8: W1201: Use lazy % formatting in logging functions (logging-not-lazy)
ci-yubi/microsign/function_app.py:26:8: W1201: Use lazy % formatting in logging functions (logging-not-lazy)
ci-yubi/microsign/function_app.py:36:8: W1201: Use lazy % formatting in logging functions (logging-not-lazy)
ci-yubi/microsign/function_app.py:46:8: W1203: Use lazy % formatting in logging functions (logging-fstring-interpolation)
ci-yubi/microsign/function_app.py:6:0: C0411: standard import "json" should be placed before third party imports "azure.functions", "azure.identity.DefaultAzureCredential", "azure.keyvault.keys.KeyClient", "azure.keyvault.keys.crypto.CryptographyClient" (wrong-import-order)
ci-yubi/microsign/function_app.py:7:0: C0411: standard import "base64" should be placed before third party imports "azure.functions", "azure.identity.DefaultAzureCredential", "azure.keyvault.keys.KeyClient", "azure.keyvault.keys.crypto.CryptographyClient" (wrong-import-order)