Allow no-passphrase private keys

[kmbenitez]

Describe the bug

The Snowflake connector (at least) requires a passphrase in the profile file to open a private key connection.

Steps To Reproduce

Create a dbt target like the following:

    qa:
      type: snowflake
      account: my_account
      user: my_user
      role: ANALYST

      # Keypair config
      private_key_path: "path/to/my/no/passphrase/key"
      private_key_passphrase: None

      database: DB
      warehouse: WH
      schema: PUBLIC
      threads: 1
      client_session_keep_alive: False

Attempt to run against said DBT target. DBT will fail because no passphrase is provided. If, instead, a passphrase is provided, the connection will fail because the key is not encrypted.

Expected behavior

Perhaps a warning in output that unencrypted keys are not the norm, requiring additional setting of override field in profile. If that's set, go ahead with the unencrypted key.

System information

Which database are you using dbt with?

• postgres
• redshift
• bigquery
• [ x] snowflake
• other (specify: ____________)

The output of dbt --version:

0.14.2

The operating system you're using:
OSX
The output of python --version:
Python 3.7.3

[kmbenitez]

I know how to just make it work within the Snowflake connection, but don't know how to do more involved things like requiring a flag in the project or profile file.

[drewbanin]

Thanks for the suggestion @kmbenitez! The operative code for private key Snowflake connections is around here:
https://github.com/fishtown-analytics/dbt/blob/31e085b7df015eac92faee4912fa481d1085c4b9/plugins/snowflake/dbt/adapters/snowflake/connections.py#L53-L65

If you have an unencrypted .pem file, would we skip the serialization.load_pem_private_key step and instead just supply raw bytes from the .pem file to p_key.private_bytes()?

If that's the case, I think we can remove the guard or self.private_key_passphrase is None and instead do something like:

if  self.private_key_passphrase is None:
  logger.warn("The specified private key is not encrypted; this is not recommended")
  p_key = ... code to get raw bytes from the file....
else:
  p_key = serialization.load_pem_private_key( ... )

I don't think we'd need extra flags in the project or profile file in this case.