Add support for LDAP Authentication

[H-LREB]

Currently, the LDAP Authentication (LDAP Auth method) is not supported by Spring Cloud Vault.

Would you consider supporting this authentication method?

I might try to submit a PR for this enhancement.

[ielatif]

@mp911de

I'm interested in contributing LDAP authentication support to Spring Cloud Vault following your recommendation from this discussion spring-projects/spring-vault#668 (comment).

I propose to support userpass, ldap, Okta and RADIUS authentication by extending a unified Properties class UsernamePasswordProperties (since they all follow the same login API pattern) while keeping specific config for each method.

/**
 * Generic properties for userpass, LDAP, Okta, and RADIUS authentication.
 */
public static class UsernamePasswordProperties {

    private String path;
    private String username;
    private CharSequence password;

    /**
     * Constructor with default path.
     */
    protected UsernamePasswordProperties(String defaultPath) {
        this.path = defaultPath;
    }

    public String getPath() {
        return path;
    }

    public void setPath(String path) {
        this.path = path;
    }

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public CharSequence getPassword() {
        return password;
    }

    public void setPassword(CharSequence password) {
        this.password = password;
    }
}

/**
 * UserPass
 */
public static class UserPassProperties extends UsernamePasswordProperties {
    public UserPassProperties() {
        super("userpass");
    }
}

/**
 * LDAP
 */
public static class LdapProperties extends UsernamePasswordProperties {
    public LdapProperties() {
        super("ldap");
    }
}

/**
 * RADIUS
 */
public static class RadiusProperties extends UsernamePasswordProperties {
    public RadiusProperties() {
        super("radius");
    }
}

/**
 * OKTA
 */
public static class OktaProperties extends UsernamePasswordProperties{

    private String totp;

    public OktaProperties() {
        super("okta");
    }

    public String getTotp() {
        return totp;
    }

    public void setTotp(String totp) {
        this.totp = totp;
    }
}	

then for the config :

# LDAP
spring.cloud.vault:
    authentication: LDAP
    ldap:
        username: myuser
        password: mypassword
        path: ldap  # Optional, auto-defaults to "ldap"

# Okta with TOTP
spring.cloud.vault:
    authentication: OKTA
    okta:
        username: myuser
        password: mypassword
        totp: 123456
        path: okta  # Optional, auto-defaults to "okta"

I can submit a PR if you're ok with this proposal.

[ielatif]

@mp911de finally only UsernamePasswordProperties was needed.
Then used for LDAP properties private UsernamePasswordProperties ldap = new UsernamePasswordProperties("ldap");