Add better documentation for the `auth login` command (#1366)

This PR improves the documentation for the `auth login` command,
accounting for the various ways this command can be used in.

---------

Co-authored-by: PaulCornellDB <paul.cornell@databricks.com>
Co-authored-by: Pieter Noordhuis <pieter.noordhuis@databricks.com>

cmd/auth/auth.go

@@ -16,9 +16,9 @@ func New() *cobra.Command {
 authentication for the Databricks CLI and SDKs work please refer to the documentation
 linked below.
 
-AWS: https://docs.databricks.com/en/dev-tools/auth/index.html
+AWS: https://docs.databricks.com/dev-tools/auth/index.html
-Azure: https://learn.microsoft.com/en-us/azure/databricks/dev-tools/auth
+Azure: https://learn.microsoft.com/azure/databricks/dev-tools/auth
-GCP: https://docs.gcp.databricks.com/en/dev-tools/auth/index.html`,
+GCP: https://docs.gcp.databricks.com/dev-tools/auth/index.html`,
 	}
 
 	var perisistentAuth auth.PersistentAuth

cmd/auth/login.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"runtime"
 	"time"
 
 	"github.com/databricks/cli/libs/auth"
@@ -32,9 +33,53 @@ func configureHost(ctx context.Context, persistentAuth *auth.PersistentAuth, arg
 const minimalDbConnectVersion = "13.1"
 
 func newLoginCommand(persistentAuth *auth.PersistentAuth) *cobra.Command {
+	defaultConfigPath := "~/.databrickscfg"
+	if runtime.GOOS == "windows" {
+		defaultConfigPath = "%USERPROFILE%\\.databrickscfg"
+	}
 	cmd := &cobra.Command{
 		Use:   "login [HOST]",
-		Short: "Authenticate this machine",
+		Short: "Log into a Databricks workspace or account",
+		Long: fmt.Sprintf(`Log into a Databricks workspace or account.
+This command logs you into the Databricks workspace or account and saves
+the authentication configuration in a profile (in %s by default).
+
+This profile can then be used to authenticate other Databricks CLI commands by
+specifying the --profile flag. This profile can also be used to authenticate
+other Databricks tooling that supports the Databricks Unified Authentication
+Specification. This includes the Databricks Go, Python, and Java SDKs. For more information,
+you can refer to the documentation linked below.
+  AWS: https://docs.databricks.com/dev-tools/auth/index.html
+  Azure: https://learn.microsoft.com/azure/databricks/dev-tools/auth
+  GCP: https://docs.gcp.databricks.com/dev-tools/auth/index.html
+
+
+This command requires a Databricks Host URL (using --host or as a positional argument
+or implicitly inferred from the specified profile name)
+and a profile name (using --profile) to be specified. If you don't specify these
+values, you'll be prompted for values at runtime.
+
+While this command always logs you into the specified host, the runtime behaviour
+depends on the existing profiles you have set in your configuration file
+(at %s by default).
+
+1. If a profile with the specified name exists and specifies a host, you'll
+   be logged into the host specified by the profile. The profile will be updated
+   to use "databricks-cli" as the auth type if that was not the case before.
+
+2. If a profile with the specified name exists but does not specify a host,
+   you'll be prompted to specify a host. The profile will be updated to use the
+   specified host. The auth type will be updated to "databricks-cli" if that was
+   not the case before.
+
+3. If a profile with the specified name exists and specifies a host, but you
+   specify a host using --host (or as the [HOST] positional arg), the profile will
+   be updated to use the newly specified host. The auth type will be updated to
+   "databricks-cli" if that was not the case before.
+
+4. If a profile with the specified name does not exist, a new profile will be
+   created with the specified host. The auth type will be set to "databricks-cli".
+`, defaultConfigPath, defaultConfigPath),
 	}
 
 	var loginTimeout time.Duration