def _validate_iat(claims):
if '<STR_LIT>' not in claims:<EOL><INDENT>return<EOL><DEDENT>try:<EOL><INDENT>int(claims['<STR_LIT>'])<EOL><DEDENT>except ValueError:<EOL><INDENT>raise JWTClaimsError('<STR_LIT>')<EOL><DEDENT>
Validates that the 'iat' claim is valid.

    The "iat" (issued at) claim identifies the time at which the JWT was
    issued.  This claim can be used to determine the age of the JWT.  Its
    value MUST be a number containing a NumericDate value.  Use of this
    claim is OPTIONAL.

    Args:
        claims (dict): The claims dictionary to validate.