feat: enable authentication

[olavloite]

Enables authentication on PGAdapter so the client can supply the credentials for a specific connection, instead of setting a fixed set of credentials on PGAdapter at startup. This also enables connecting to different Google Cloud projects and instances. The database property in the connection parameters may be a simple database id (e.g. my-database) or a fully qualified database name (e.g. projects/my-project/instances/my-instance/databases/my-database).

The credentials must be one of the following:

1. The private key string of a service account. This string must include the -----BEGIN PRIVATE KEY----- and -----END PRIVATE KEY----- headers. The username must be the email address of the service account.
2. The JSON contents of a Google credentials file. This could be a service account file or a user account file. The credentials file is sent in the password message. The username is ignored.

[codecov]

Codecov Report

Merging #174 (3fd7251) into postgresql-dialect (e3016d1) will increase coverage by 0.67%.
The diff coverage is 81.63%.

@@                   Coverage Diff                    @@
##             postgresql-dialect     #174      +/-   ##
========================================================
+ Coverage                 78.87%   79.55%   +0.67%     
- Complexity                 1011     1043      +32     
========================================================
  Files                        89       91       +2     
  Lines                      3494     3560      +66     
  Branches                    406      422      +16     
========================================================
+ Hits                       2756     2832      +76     
+ Misses                      578      566      -12     
- Partials                    160      162       +2     

Flag	Coverage Δ
all_tests	79.55% <81.63%> (+0.67%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ud/spanner/connection/ConnectionOptionsHelper.java	50.00% <50.00%> (ø)
...panner/pgadapter/wireprotocol/PasswordMessage.java	58.97% <58.62%> (+58.97%)	⬆️
...utput/AuthenticationCleartextPasswordResponse.java	71.42% <71.42%> (ø)
...ud/spanner/pgadapter/metadata/OptionsMetadata.java	84.93% <92.10%> (+4.20%)	⬆️
...gle/cloud/spanner/pgadapter/ConnectionHandler.java	76.52% <100.00%> (+0.08%)	⬆️
...ud/spanner/pgadapter/wireoutput/ErrorResponse.java	94.04% <100.00%> (+0.14%)	⬆️
...spanner/pgadapter/wireprotocol/StartupMessage.java	85.36% <100.00%> (+19.57%)	⬆️
... and 1 more

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[aseering]

@guangylegend I wonder if this change to PGAdapter would be sufficient to enable running multiple Spangres tests against multiple databases (in the same local instance) using a single PGAdapter, like we just talked about earlier today?

Anyway -- I am by no means a qualified Java reviewer, but overall this change seems reasonable.

[olavloite]

@guangylegend I wonder if this change to PGAdapter would be sufficient to enable running multiple Spangres tests against multiple databases (in the same local instance) using a single PGAdapter, like we just talked about earlier today?

You actually don't need this change for that, as that is already supported. If you start PGAdapter without a -d (database) command line argument, PGAdapter will connect to the database that is given in the connection request. Note that this does mean that you must include a database in the connection request when you start for example psql.

This change will however also add support for connecting to different databases on different instances or even in different projects, as it will add support for fully-qualified database names in the connection request.