update: add password auth and passphrase support to documentation

- Update man page with password flag and passphrase information
- Add authentication section to README with examples
- Improve help text for identity flag to mention passphrase support
- Keep version number unchanged at 0.3.0

Author: inureyes

Cargo.lock

@@ -55,6 +55,38 @@ bssh -c production ping
 bssh list
 ```
 
+## Authentication
+
+bssh supports multiple authentication methods:
+
+### SSH Key Authentication
+- **Default keys**: Automatically tries `~/.ssh/id_ed25519`, `~/.ssh/id_rsa`, `~/.ssh/id_ecdsa`, `~/.ssh/id_dsa`
+- **Custom key**: Use `-i` flag to specify a key file
+- **Encrypted keys**: Automatically detects and prompts for passphrase
+
+### SSH Agent
+- **Auto-detection**: Automatically uses SSH agent if `SSH_AUTH_SOCK` is set
+- **Explicit**: Use `-A` flag to force SSH agent authentication
+
+### Password Authentication
+- Use `-P` flag to enable password authentication
+- Password is prompted securely without echo
+
+### Examples
+```bash
+# Use default SSH key (auto-detect)
+bssh -H "user@host" "uptime"
+
+# Use specific SSH key (prompts for passphrase if encrypted)
+bssh -i ~/.ssh/custom_key -c production "df -h"
+
+# Use SSH agent
+bssh -A -c production "systemctl status"
+
+# Use password authentication
+bssh -P -H "user@host" "ls -la"
+```
+
 ## Configuration
 
 ### Configuration Priority Order

README.md

@@ -14,8 +14,9 @@ bssh \- Backend.AI SSH - Parallel command execution across cluster nodes
 is a high-performance parallel SSH command execution tool for cluster management, built with Rust.
 It enables efficient execution of commands across multiple nodes simultaneously with real-time output streaming.
 The tool provides secure file transfer capabilities using SFTP protocol for both uploading and downloading files
-to/from multiple remote hosts in parallel. It automatically detects Backend.AI multi-node session environments 
-and supports various configuration methods.
+to/from multiple remote hosts in parallel. It supports multiple authentication methods including SSH keys (with
+passphrase support for encrypted keys), SSH agent, and password authentication. It automatically detects Backend.AI
+multi-node session environments and supports various configuration methods.
 
 .SH OPTIONS
 .TP
@@ -37,7 +38,8 @@ Default username for SSH connections
 
 .TP
 .BR \-i ", " \-\-identity " " \fIIDENTITY\fR
-SSH private key file path
+SSH private key file path. If the key is encrypted, bssh will
+automatically prompt for the passphrase.
 
 .TP
 .BR \-A ", " \-\-use\-agent
@@ -46,6 +48,12 @@ When this option is specified, bssh will attempt to use the SSH agent
 for authentication. Falls back to key file authentication if the agent
 is not available or authentication fails.
 
+.TP
+.BR \-P ", " \-\-password
+Use password authentication. When this option is specified, bssh will
+prompt for the password securely without echoing it to the terminal.
+This is useful for systems that don't have SSH keys configured.
+
 .TP
 .BR \-p ", " \-\-parallel " " \fIPARALLEL\fR
 Maximum parallel connections (default: 10)
@@ -205,6 +213,20 @@ Use custom SSH key:
 Use SSH agent for authentication:
 .B bssh -A -c production "systemctl status"
 
+.TP
+Use password authentication:
+.B bssh -P -H "user@host.com" "uptime"
+.RS
+Prompts for password interactively
+.RE
+
+.TP
+Use encrypted SSH key:
+.B bssh -i ~/.ssh/encrypted_key -c production "df -h"
+.RS
+Automatically detects encrypted key and prompts for passphrase
+.RE
+
 .TP
 Save output to files:
 .B bssh --output-dir ./results -c production "ps aux"
@@ -299,8 +321,9 @@ User configuration directory location
 SSH known hosts file for host key verification
 
 .TP
-.I ~/.ssh/id_rsa
-Default SSH private key
+.I ~/.ssh/id_ed25519, ~/.ssh/id_rsa, ~/.ssh/id_ecdsa, ~/.ssh/id_dsa
+Default SSH private keys (checked in order of preference). If a key is
+encrypted, bssh will prompt for the passphrase.
 
 .TP
 .I $SSH_AUTH_SOCK

docs/man/bssh.1

@@ -47,7 +47,7 @@ pub struct Cli {
     #[arg(short = 'u', long, help = "Default username for SSH connections")]
     pub user: Option<String>,
 
-    #[arg(short = 'i', long, help = "SSH private key file path")]
+    #[arg(short = 'i', long, help = "SSH private key file path (prompts for passphrase if encrypted)")]
     pub identity: Option<PathBuf>,
 
     #[arg(