v2.21.0

• refactor ADFS provider to support AzureMFA as well #380
• (readme) Linux installation notes #385
• Fix Okta MFA regression issue #387
• Added Akamai for command line idp-provider #391
• fix aad Response did not contain a valid SAML assertion #381
• OneLogin API credential is received as an argument during login #394
• Adds WebAuthn support for Okta using U2F #389
• Move from alsmola/go-u2fhost to marshallbrekka/go-u2fhost #396